When ABC switched both “China Beach” and “Twin Peaks” to Saturday night this season, the web hoped to mine what it calls an untapped audience of 30-to 45-year-olds.

But “China Beach” soon was gone, replaced by “Under Cover,” and last week both “Under Cover” and “Twin Peaks” were yanked from Saturdays.

Despite these failures, ABC remains confident about its recent deal with MTV and sister net Nickelodeon to create primetime programming for baby-boomers on Saturday night.

“Saturday night has always been a self-fulfilling prophecy,” says Alan Wurtzel, ABC’s senior v.p., research. He says the reason most Saturday-night shows draw an older crowd, one not coveted by advertisers, is “the networks put on shows with the least potential. The conventional wisdom was that anyone under 50 was out, so we should go for the older audiences.”

Most teenagers and twentysomethings are out on Saturday night, but a recent ABC study maintains that more and more baby-boomers – a group not distinctly charted in Nielsen demos – are staying home. “But it is still the most difficult group to attract, and they are the most fickle,” Wurtzel acknowledges.

“China Beach” was too “heavy” for Saturday night, he says. And even if baby-boomers are spending more Saturdays at home, they are not going to be in front of the tv every Saturday, Wurtzel says, explaining the downfall of what he calls “a complicated serial” like “Twin Peaks.” “It is silly to assume people are going to change their behavior irrevocably to watch a tv show,” he says.

“Twin Peaks” initially doubled ABC’s numbers for young adults in that time slot, Wurtzel adds, proving that the potential is there. “It is just a matter of finding the right program.”

The theory is lent some credence by the shifting demos of NBC’s “Saturday Night Live.” According to figures supplied by Nielsen Media Research, the show had 4.8 million 18-34 viewers in only 5.6 million households for the period from September 1976 to Jan. 9,1977. This season, through Jan. 6, “SNL” is in 6.8 million households; it has lost 21% of those 18-34 viewers, but the 25-54 crowd grew 27% to 5.7 million from 4.5 million.

“There are viewers available,” agrees Steve Sternberg, v.p. of broadcast research for the ad agency Bozell Inc. “With something creative that skews young, they might be able to pull viewers away… the way ‘The Simpsons’ did on Thursday.”

NBC’s Friday night success with “Miami Vice” in the mid ’80s proves conventional weekend wisdom can be defied, says Bob Niles, senior v.p. of research for NBC. “For a few years it caught fire and the target audience was watching it,” he says.

But Niles warns that some advertisers, especially movie companies, want to capture younger audiences midweek to influence their weekend plans. Viewers sitting home watching tv on a Saturday night are not considered as valuable an audience.

And even if there is a potential baby boomer audience on Saturday nights, that doesn’t guarantee high ratings for an ABCMTV show, since 20% of all VCR primetime playback is done Saturday night, the most of any night of the week, according to Bozell Inc’s Sternberg.

ABC acknowledges that standard programming will continue losing viewers to the VCR. “For a couple of bucks you can get a $30 million movie,” Wurtzel says. “What is it you can’t rent?”

ABC is counting on its original programming with MTV to be the unique blend of variety, music and comedy that can lure boomers back to network tv.

Wurtzel says Saturday is a good time to experiment, calling it a “minimal risk night.”

CBS agrees that traditional sitcoms and dramas no longer are viable for attracting the 18-49 group on Saturday nights, but its solution is less ambitious and more pragmatic than ABC’s.

“Everything we had there previously didn’t work,” says Michael Eisenberg, CBS v.p. of audience measurement, referring to programs like the post-Ken Wahl “Wiseguy” and “Broken Badges.” The 18-34 viewers aren’t home, the 55-plus crowd watches NBC, and the audience in between abandoned tv for rented movies, so CBS attacked the problem with the “Saturday Night Movie,” he says.

“With ‘Dirty Dancing,’ we had our best Saturday of the year,” Eisenberg says of the Feb. 9 broadcast, adding that in its final half-hour, the film was No. 1 with women 25-54 and men 18-49. “Once ‘Golden Girls’ and ‘Empty Nest’ are out of the way, we pick up a sizable audience.”

Niles is skeptical of ABC’s Saturday-night niche programming, pointing out that while NBC’s shows skew toward older, more loyal audiences, they are popular enough to have broad appeal.

For instance, “Golden Girls” consistently defeated its competition for male and female 18-34 viewers, ranging from 1.4 million to 2.5 million for males, and 2.5 million to 3.8 million for females (Nielsen, Sept. 17 to Dec. 30,1990). Five “Golden Girls” episodes in that period drew more women 18-34 than the episode of “Twin Peaks” when Laura Palmer’s killer was revealed. Except for that week in November, NBC’s head-to-head competitor, “Carol And Company,” generally matched “Twin Peaks” in men 35-54 and women 18-34 and was stronger with women 35-54.

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