A new advertising campaign launched last week in San Francisco aims to educate gay men in the city about the links between crystal methamphetamine use and HIV infections. The campaign includes a series of ads featuring images of gay men tweaking and engaging in high-risk sexual behavior after taking crystal meth. The ads carry the tagline "Crystal Mess" and point out that gay men who use crystal are 400% more likely to become infected with HIV through risky sexual activity than nonusers. The ads appear in bus shelters and billboards in the city as well as through "guerrilla marketing techniques" in the city's Castro and South of Market neighborhoods, campaign officials say. San Francisco health officials say they hope the campaign's frank language and imagery promote discussions about crystal meth use among gay men visiting and living in the city. The campaign, which runs through November 21, was timed to coincide with the city's annual Castro Street Halloween celebration. A similar media campaign was conducted earlier this year in New York City.