On the widely used Web site Craigslist.org, some landlords and apartment dwellers looking for roommates are offering to accept sex in lieu of rent.

"They have to be attractive. I don’t let just anybody come into my house," said Mike, a man who answered the phone at the New York City listing but declined to give his last name, and refused to say whether he has, in fact, collected the rent under the sheets.

The offering of shelter for sex is older than, well, real estate itself.

But the online come-ons are franker than anything you might see in the newspaper classifieds, because they are not edited by Craigslist, and perhaps also because the anonymity of the Internet often causes people to shed their inhibitions.

Trading housing for sex is a form of prostitution. But the police aren’t kicking down doors.

Paul J. Browne, a deputy police commissioner in New York, said investigators have found that the Craigslist ads are frequently "little more than a form of voyeurism that didn’t result in an actual exchange of sex for rent."