To better target efforts aimed at modifying sexual behaviour among injecting drug users (IDUs), we conducted a detailed analysis of sexual partners and practices reported by 1214 Italian heterosexual drug users during the period June 1985-June 1987. Females were more likely to have only drug-using partners (42.8% vs 17.1%), while males were more likely to have only non drug-using partners (50.5% vs 21.4%). Female drug users were more likely to report either one partner or greater than 10 partners, while males were more likely to report 2-10 partners. Nearly 90% of women with only drug-using partners had only one partner. Overall, 29% of women with only non drug-using partners reported that they always used condoms. This proportion increased to 65% among women with greater than 10 non drug-using partners. In Italy, male IDUs may play a greater role than female IDUs in sexual transmission of HIV infection to the heterosexual non drug-using partners.