This study examined differences in drug use, sexual behavior, attitudes, and perceptions of vulnerability for AIDS between injection drug users who received methadone treatment in the previous 6 months and those who did not. Of the 123 participants assessed, 62 (50%) received methadone treatment. Methadone patients reported fewer sexual partners and greater use of condoms compared to nonmethadone patients. Methadone patients also reported fewer high-risk sexual partners than those not in treatment. Women reported more high-risk partners than men. Methadone patients reported drinking alcohol less, but smoking marijuana more than nonmethadone users. Methadone users had more positive beliefs about the efficacy of condoms for preventing AIDS and expressed less anger than nonmethadone users in situations related to condom usage. These findings have important implications for using methadone maintenance to reduce the dual risk for HIV in injection drug users.