Methadone maintenance has been found to be effective in reducing intravenous drug use, a primary means for transmitting the AIDS virus. This study examined the association between length of time under continuous MMTP treatment and risk behaviors such as frequency of drug injection, frequency of injection in shooting galleries, and frequency of sharing drug equipment. It also determined the number of sex partners and the number of sexual partners who were not intravenous drug users. Data were obtained through private interviews using a structured questionnaire. Although many intravenous drugs users currently enrolled in MMTP's continue to engage in drug transmission behaviors that could transmit the AIDS virus, MMTP's are nevertheless effective in reducing these behaviors. Those who have been in MMTP's longer are less likely to use drug injection. MTP's, however, do not apparently affect the frequency of sexual contact nor the number of steady sexual partners who are not intravenous drug users. 6 tables 9 references.