In 1984, NBC was beginning its fall season in a position that had become all too familiar: It was dead last in the ratings derby of the big-three networks.
But one comedy about an upscale black family living in New York changed the landscape of Thursday nights when it made its debut that year.
It was The Cosby Show, which won its time period from its initial run and took NBC from worst to first in just two years, a perch NBC tightly held onto through the next six years.
"Cosby came in and revolutionized Thursday nights," said Dave Davis, an analyst with Paul Kagan Associates, a firm that places television ads for its clients.
Building on the strength of the Huxtable clan, NBC's Thursday night lineup was a powerhouse through the '80s and into the '90s, with such shows as Family Ties, Cheers and Hill Street Blues in earlier years, to L.A. Law, A Different World and now Wings, all top-20 shows.
But NBC's glory days might be behind it, with Cosby leaving the air after its eighth season and with Cheers entering what has to be difficult _ and expensive _ negotiations to bring it back for an 11th year.
"NBC is losing momentum," said Hank Cohen of KSL Media, a New York media-buying firm. "They're going to have a tough time keeping that night."
Though Davis still thinks NBC will hang onto Thursdays next year, he readily admits the network will have a steep climb ahead of it. He points to A Different World, Cheers and Wings, which routinely are ahead of Cosby in the ratings.
"It shows even when Cosby leaves, NBC will still have strength on Thursday nights, and they will still be the network to beat," he said.
Challengers to Thursday nights are many. Fox Broadcasting Co. made a bold move two years ago when it scheduled The Simpsons, its hip, animated comedy, on Thursdays against Cosby.
While Cosby still regularly trounces The Simpsons, there's no doubt that it has eroded the once seemingly invincible No. 1 ratings pulled in by the Huxtable household.
But it took a long time for any show to put a dent in Cosby's ratings. "The Simpsons gave Cosby the first run for its money in quite a while," said Davis.
And then there is the other Fox phenomenon, Beverly Hills, 90210, a drama that is earning its stripes among teens and young adults, the ages most coveted by the advertisers who sponsor the show.
KSL's Cohen said Fox is successful precisely because it went after the right audience.
"They went after the audiences advertisers are going after, the 18-to-34 (age group). They weren't as conservative in their approach. They risked a little bit more. They're definitely a player to be reckoned with. They're offering the audience," Cohen said.
Over at ABC and CBS, both have relatively low-cost shows to schedule in against NBC and Fox.
"Everyone is counterprograming rather effectively," said Betsy Frank, senior vice president and director of television information and news media for Saatchi and Saatchi in New York.
ABC is plugging in two hours of Columbo reruns from 8 to 10 p.m. following up with PrimeTime Live, a news program that is cheaper to produce than comedy or drama series.