This FIRST Award proposal seeks five years of support to: (1) develop and test methods of assessing and reducing social desirability response biases in self-reporting in samples of injecting drug users who are infected with or at high risk for HIV, and (2) to systematically assess a specially developed social influence model to explain changes in HIV risk behaviors in urban African American men and women. The previously collected reports of drug use, medical records, HIV status, and hospitalization records from the ALIVE and SAFE studies will be used both in the study on methods of reducing the social desirability response bias in injecting drug users and in the social influence model as potential validating evidence of self-reported measures of changes in HIV risk behaviors. The main elements of the social influence model will focus on influences on individual risk behaviors on the following: social network characteristics, group norms, and behavioral settings. Social network analyses will be conducted on preexisting data from an ongoing study (SAFE), an experimental preventive intervention for IDUs which uses a social network approach. The model will be confirmed using new data collected from ALIVE study and SAFE study subjects. The ALIVE study is a longitudinal study of the natural history of HIV in injecting drug users.