BALTIMORE, Md. - Pornography is not a mainstream business, but even so, more and more adult film actors are turning up in Hollywood movies.

Kobe Tai appears in Very Bad Things as a stripper in the bachelor party scene, Ron Jeremy turns up in the disco movie 54, Asia Carrera plays a porn star in The Big Lebowski, and Heather Hunter and Chasey Lain portray call girls in the Spike Lee film He Got Game.

The question is: What are they doing there?

Adding spice, frankly. Having a porn star play a porn star doesn't just add verisimilitude. It's also a nudge-wink acknowledgment by the film's makers that the audience knows what porn stars are supposed to look like and that people might even recognize a few.

Watching pornography, after all, is the U.S. entertainment industry's biggest dirty secret. Trade magazine Adult Video News (AVN) says an estimated 8,948 hard-core titles were released on video in 1998, an increase from 7,970 the year before. Those tapes would account for $819 million (U.S.) in wholesale sales.

You won't find any of the titles at Blockbuster. But for video shops that rent adult tapes, porn usually accounts for a healthy chunk of the inventory - an average of 19.7 per cent, according to AVN. Some 686 million X-rated titles were rented in the United States last year, a figure that makes it easier to understand why so many viewers recognize Jeremy and his colleagues. But even though a lot of people are renting those tapes, it isn't politic to say so.

As Carrera puts it: "The general public does not want to admit that they know who any porn stars are."

That's beginning to change as a generation bred on shock jocks, music videos and VCRs constitutes an increasingly large part of the movie-going public.

"I think my generation is a lot more loose-lipped about watching porn," says David Schlesinger, 26, the director of public relations at Vivid Video, an adult-film company based in Los Angeles. "It's not unusual to go to a party with a lot of people there, and there's music on the stereo, and a porno in the VCR. It's really no big deal."

Jeremy is a porn industry legend who has acted in or directed more than 1,200 adult films, and had roles in 28 mainstream pictures. "When it comes to the youth, the guys always know me," he says.

"I did comedy at some clubs, and it really was brought home then that the guys know me but the girls don't. But then when the girls get older, into their 20s and 30s, they tend to know me also because they've seen the films with their boyfriends."

Shock jock Howard Stern has been inviting adult film stars on his radio show for years, turning the likes of Lexus and Janine into drive-time celebrities. The music video industry has been friendly to porn stars and directors. The latest Metallica video, Turn The Page, features mock-documentary footage of former porn star Ginger Lynn as a down-on-her-luck exotic dancer.

Still, it's unlikely the adult film industry will ever be accepted as mainstream entertainment. "To me, porno films are the last outlaw cinema left," says director John Waters, who hired former porn star Traci Lords for the 1990 Johnny Depp film, Cry-Baby.

Before Waters cast her, Lords had been at the centre of the worst scandal ever to hit the porno business. Lying about her age, she posed for nude photographs at age 15, graduating to porn movies a year later. By the time authorities found out she had been using a fake birth certificate, the then-17-year-old had made dozens of videos, all of which were seized and subsequently destroyed as child pornography.

Acting ability - or a lack thereof - is one of the biggest issues for adult film actors trying to cross over into the mainstream. "Porn stars aren't taken very seriously as actresses," Carrera says.

Nor are porn actors typically given demanding roles. "Get murdered or be a hooker," says Waters, summing up the range of parts offered to adult film actresses in mainstream films. "A big stretch, these roles."