With a few notable exceptions, network television has largely avoided sciencefiction/fantasy shows over the past few years.

"The X-Files" was a big hit on Fox, and "Buffy," "Angel" and various "Star Treks" have found more limited success on smaller networks UPN and the WB. But, for the most part, shows in the "genre" (as it's known) have mostly been found on cable and in syndication.

But there's a mini-revolution of sorts going on this fall. A total of six new sci-fi/fantasy shows are on ABC, CBS, NBC and the WB's schedules, joining returning shows "Lost," "Medium," "Smallville" and "Charmed."

Aliens (of one kind or another) are invading on "Invasion" (ABC), "Surface" (NBC) and "Threshold" (CBS).

Ghosts, demons and monsters abound on "Supernatural" (WB), "Ghost Whisperer" (CBS) and "Night Stalker" (ABC).

"Genre is tricky, but when it hits, it can hit huge," said NBC Entertainment president Kevin Reilly, who pointed to the "Lord of the Rings" movies as a prime example. "When you get crossover people, then you can really break out."

COULD THE SUCCESS of one series last season have had such a profound effect on what we're seeing this season? Some people certainly think so.

"I think you can answer that question in three words — 'Lost,' 'Lost' and 'Lost,' " said Shaun Cassidy, the creator/executive producer of "Invasion," adding that ABC's hit "has changed the climate for shows that don't answer all your questions at the end of every episode."

"It didn't hurt," said "Threshold" executive producer David Goyer, and "Surface" executive producer Josh Pate called the theory "valid."

However, other executives at competing networks were not so quick to point to ABC's "Lost" as the reason they've put sci-fi/fantasy shows on their schedules this fall.

"It was certainly part of my plan coming in the door — let's do some bigger ideas," NBC's Reilly said. " 'Lost' kind of beat us to the punch with that a little bit by making one stick."

"We don't literally go out to the (creative) community and say, 'Because that particular show is successful on another network, please bring us that," said CBS Entertainment president Nina Tassler, who insisted her network has had sci-fi shows "every year in development," but that "Threshold" and "Ghost Whisperer" just happened to be "terrific."

"For us, it was based on producing the best pilot scripts that we had," Tassler said.