But the new wave of sexually oriented games represents a major shift because major players like Nintendo and Sony are taking the plunge.

For Nintendo, the decision to go down the naughty road comes after years when it seemed to go out of its way to avoid offending gamers (or their parents). The company was among the first to set stringent guidelines for child-friendly gaming, like changing blood color from red to green or, more curiously, in Wolfenstein 3D, substituting rats for guard dogs as shooting targets.

Perrin Kaplan, vice president of corporate affairs for Nintendo, said there was a feeling within the company that it had to do more for its gamers as they grew older.

''One of the things Nintendo has been criticized for is just being a kiddy system,'' she said. ''People who fell in love with Mario at the age of 6 are now in their 30's. They have expectations of Nintendo that we have not met.''

The green light for Conker's Bad Fur Day came in great part, Ms. Kaplan said, because of the reputation of the game's developer, a reclusive and idiosyncratic company called Rare that was started by two brothers in the English countryside. From its office near the village of Twycross, Rare has churned out some of Nintendo's biggest hits in recent years, including two acclaimed M-rated shoot-'em-up games, GoldenEye and Perfect Dark, as well as the E-rated (for everyone) Donkey Kong Country and Banjo-Kazooie.

The character of Conker had already had a bit part in earlier games when Rare brought up the idea of a starring vehicle for the puckish squirrel. The developers wanted to use him as, essentially, a personification of the adult gamer.

''I think the best way to view Conker with respect to his earlier incarnations is that like people, he's changed and matured -- or become more cynical -- with age,'' an unnamed developer from Rare (they prefer anonymity) told Amazon.com in an uncustomary interview earlier this year. Rare officials declined to be interviewed for this article.