Male clients of prostitutes have proved to be a very difficult group to access for the purposes of HIV research and education. Prevention initiatives to date have placed less emphasis on HIV awareness with this potential target group and more on empowering prostitutes to control the sexual transaction with clients. Data is presented from a study of male clients of prostitutes, conducted as part of a wider study of drug using and nondrug using prostitutes in the Greater Manchester area during 1991-92. The study focuses on sexual activities and risk behaviours of male clients with female prostitutes, and with regular and casual partners. The data provides evidence of high levels of risk-taking, particularly by bisexual clients. Implications for research and HIV prevention are discussed. It is concluded that placing the major burden for behaviour change on prostitutes themselves may have only a limited effect and that other involved persons (including clients) should be more actively targeted in the development and implementation of STD/HIV prevention.