NEW YORK -- If you listen carefully amid the applause for Johnny Carson as he prepares to leave late-night television after 30 years, you might hear the sound of cash registers ringing.
Between now and May 22, when the final "Tonight Show Starring Johnny Carson" will run, NBC will raise its rates for a 30-second commercial, in stages, about fivefold -- yes, fivefold -- to almost $200,000 for the finale.
That instant inflation from the regular price of $40,000 will place the show's rates on a par with what marketers like Miller Brewing and Wendy's might pay for a 30-second commercial on a hit prime-time series like "Roseanne." But it is still far below the $850,000 it cost for a 30-second spot during Super Bowl XXVI in January.
The reason for the hefty price tag for Mr. Carson's farewell, of course, is clear: NBC anticipates that the show's normal audience of about 10 million will swell to about 35 million for the finale, said Curt Block, a network spokesman in New York. That would be the second-largest audience ever for "Tonight," after the 58 million who tuned in on Dec. 17, 1969, to watch the singer Tiny Tim marry his Miss Vicki.
The transition from Mr. Carson to his designated successor, Jay Leno, has been as carefully orchestrated as the media hoopla surrounding the abdication of the "king of late night." After all, in a medium that has witnessed the cancellation of a series after but a single episode, three decades is more of a reign than a run. Mr. Carson announced his impending retirement last May, followed a month later by NBC's selection of Mr. Leno, who has been his regular substitute host since 1987, as his replacement, effective May 25.
Still, advertising and media executives are watching intently for signs of disruption following Mr. Carson's record stint as host of a show that routinely generates annual advertising revenues of $100 million.
Many expressed the belief that ratings for "The Tonight Show With Jay Leno," as it will be called, will slip to some degree compared with Mr. Carson's. But most of them do not expect any giant defections.