The purpose of this paper is to assess sexual behaviours which place heroin sniffers (HSs) at high risk for HIV infection. A stratified network-based sample was used to recruit HSs who had no history of injection drug use was recruited from the streets of South Florida, USA. HSs displayed a high HIV seroprevalence rate of 12.1%; women (18.1%) were more likely than men (8.7%) to test positive for HIV. Both men and women HSs engaged in considerable high risk sex behaviour, including high risk sex-exchange behaviour. The use of crack cocaine was associated with increased sex exchange behaviour among women. The need for intervention programs targeted toward HSs is discussed.