It is commonly assumed that people who are addicted to certain substances would abuse any substance. This position has never been supported by validly collected and analyzed research data. In this study, the authors examine the use of street methadone by heroin addicts seeking their first agonist opioid treatment in a clinical setting. Fifty-four heroin addicts who resorted to street methadone use were compared by socio-demographic, current clinical, and disease-related variables to 251 peers who do not use street methadone. Heroin addicts who resort to street methadone use are more likely to be females and to have a higher degree of education, are less likely to engage in polyabuse (use of more than three substances), are less severely ill, have been addicted for a shorter period of time, and have been seeking treatment sooner in the course of their disease. Also, they suffer from a wider range of psychopathological distress symptoms. In Italy, resorting to street methadone does not seem to be a surrogate form of heroin addiction, but rather represents means of harm reduction, with treatment seeking occurring shortly after its initiation. This should be accounted for when deciding on take-home policies and issues of potential methadone diversion.