This paper presents a qualitative investigation of peer mentoring among HIV seropositive injection drug users in a randomized controlled trial, the INSPIRE study. Qualitative analyses of 68 in-depth open-ended interviews conducted in 2005 in Baltimore, New York, Miami, and San Francisco revealed that these individuals conceptualized themselves as change agents through the identity of peer mentor at the three related domains of individual, interpersonal, and community-level change. Implications for program development and future research of peer mentoring as a mechanism for HIV prevention are discussed. This study was funded by the Centers for Disease Control and Prevention and Health Resources and Services Administration (HRSA).