BOB GARFIELD: Last weekend's surprise box office favorite was "Freddy Vs. Jason" which took in more than 36 million dollars despite the blackout. We're still waiting to see if the success of linking two movie franchises sparks a real trend -- say Austin Powers teaming up with James Bond or Shaft hunting down Blacula, but as NPR's Jim Zarroli reports, the appeal of the crossover is something that TV producers have long understood.

JIM ZARROLI: The first thing Thom Holbrook would have you know is that a crossover is not the same thing as a spinoff. A spinoff is when a popular character from one TV show gets his or her own show. Good Times was a spinoff of Maude which was a spinoff of All in the Family. A crossover, says Holbrook, is something altogether different.

THOM HOLBROOK: It's not necessarily a character from one show leaving to start another show. It's a character from one show paying a little visit to another show.

JIM ZARROLI: For instance he says the character of Kramer on Seinfeld once showed up as Murphy Brown's secretary. The character of Chandler on Friends appeared on Caroline in the City. And Bobby from The Practice ran in to Ally McBeal -- literally. [TWO PEOPLE BUMP INTO EACH OTHER]

BOBBY DONNELL: Are you all right?! Are, are you okay?!

ALLY McBEAL: Oh! It's - I just get--

BOBBY DONNELL: I wasn't looking where I was going.

ALLY McBEAL: It's, it's okay.

BOBBY DONNELL: Bobby Donnell.

ALLY McBEAL: Ally Donnell - M--M--McBeal.

JIM ZARROLI: A few years ago, Holbrook was working at a TV station in Ohio. His job entailed watching lots of old reruns. And he came to realize just how venerable a tradition the crossover is in television. Charlie's Angels did a crossover with the Love Boat. Alice did a crossover with the Dukes of Hazzard. There was even an animated crossover between Bewitched and the Flintstones. [FLYING THROUGH THE AIR WHISTLE]

SAMANTHA: Bye. Have fun.

WILMA: Hi! We're your new neighbors! I'm Wilma Flintstone and this is Betty Rubble.

SAMANTHA: Nice to meet you! I'm Samantha. [VEHICLE ENGINE] And that's my husband, Darren.

JIM ZARROLI: In fact, there were crossovers way back in the days before color TV. Private Secretary once did a crossover with the Lucy-Desi Comedy Hour which crossed over with Make Room for Daddy which crossed over with the Dick Van Dyke Show. Some of the best television writers and producers -- people like Steven Bochco and David E. Kelley have filled their programs with crossovers and sly references to each other. But much of the time crossovers are little more than a ratings stunt -- a way for a network to promote one show at the expense of another. Larry Jones is General Manager of TV-Land which periodically does whole evenings of crossovers and spinoffs.

LARRY JONES: After a show's been on a while, it's like how do you get people in the third or fourth season, how do you get people to continue that excitement about the show, how do you keep people talking about it around the water cooler. Here's another way -- oh! Look, though - they're doing this week - they're doing something else - it's something different.

JIM ZARROLI: But there may also be something fundamentally appealing to viewers about the notion that characters from different programs exist on the same existential plane. Jones says it goes to television's place in the American psyche.

LARRY JONES: We often talk about TV Land not in the sense of like this-- cable channel, but TV Land in the generic form of like there's this place that exists out there where Donna Reed lives down the street from, you know, Leave It To Beaver. You know, Joe Mannix is the guy you go to when, you know, you need an investigator. You kind of do think shows of a certain ilk -- they probably did know each other. They probably did live down the block.

JIM ZARROLI: For Thom Holbrook there's also a six degrees of separation kind of appeal to crossovers. A few years ago he set out to list how many crossovers he could find. At first he used charts. Then he set up his own web site. After it was named Yahoo's Site of the Week he heard about even more crossovers. Holbrook never lists a crossover on his site unless he can verify its accuracy. But there are hundreds of verifiable crossovers connecting dozens of programs to each other.

THOM HOLBROOK: The end result is you can have shows utterly far-removed from each other connected in the same world such as-- my prime example always is you can connect the world of the sitcom M*A*S*H to the world of X-Files.

JIM ZARROLI: Holbrook says the character of BJ Hunnicut on M*A*S*H was once mentioned as a medical school friend of one of the doctors on St. Elsewhere. The St. Elsewhere character of Roxanne, played by Alfre Woodard appeared on an episode of Homicide. The Homicide's Detective Munch turned up on the X-Files interrogating a character.

DETECTIVE MUNCH: Detective Munch, Baltimore Homicide.

MAN: Did they find her?

DETECTIVE MUNCH: And a good evening to you! Sorry, no sign of your mystery lady.

MAN: She is real. The FBI agent saw her.

DETECTIVE MUNCH: Yeah, well Special Agent-- Mulder is currently being held in five-point restraints, jabbering like a monkey.

JIM ZARROLI: Holbrook says he can connect Knight Rider to Star Trek; Touched by an Angel to Mannix and Gomer Pyle to NYPD Blue. Sometimes the connection is subtle. The hospital on St. Elsewhere was taken over by the Weigert Medical Corporation which was also the name of the company that ran the prison hospital on Oz. Both shows were written by Tom Fontana who does a lot of crossovers. Holbrook says that at times the currents and crosscurrents between different programs get positively mind-bending. For instance, he says, in the last episode of St. Elsewhere the entire series was revealed as the dream of an autistic boy. But St. Elsewhere crossed over with a lot of other shows. Were they also part of the boy's dream, he asks? Complicating it all is the fact that one of St. Elsewhere's crossovers was the Bob Newhart Show in which the comic actor played a Chicago psychologist. It later had a very memorable crossover of its own with the actor's next sitcom called Newhart.

THOM HOLBROOK: And the last of episode of Newhart revealed that that entire series had been the dream of his character from the Bob Newhart Show. So now you have a s-- a case where you have a young autistic boy not just dreaming an entire reality; he's also dreaming about a psychiatrist who dreamed an entire 'nother universe.

JIM ZARROLI: And what of the fact that Newhart crossed over with shows of its own? Is the entire TV universe one of separate realities that overlap and double back on themselves in a way that makes quantum physics look simple? Holbrook says that may be the point at which you've probably carried crossover analysis a little too far. For On the Media this is Jim Zarroli. [THEME MUSIC]

BOB GARFIELD:That's it for this week's show. On the Media was produced by Janeen Price, Katya Rogers, Tony Field and Megan Ryan; engineered by Rob Christiansen, Dylan Keefe, George Edwards and Neal Rauch and edited-- by Brooke. We had help from Blake Carlton and Josh Keating. Our webmaster is Amy Pearl.

BROOKE GLADSTONE:Arun Rath is our senior producer and Dean Cappello our executive producer. Bassist/composer Ben Allison wrote our theme. This is On the Media from NPR. I'm Brooke Gladstone.

BOB GARFIELD: And I'm Bob Garfield.