As part of Phase II of the World Health Organisation (WHO) Injecting Drug Use Multi-City Study, Rapid Assessment and Response (RAR) methodology was used in São Vicente City (São Paulo State, Brazil) to analyse the situation regarding injecting drug use and HIV infection. Over a period of 8 weeks, analysis of existing information, focus groups (four) and depth interviews (45) were conducted, with qualitative data analysis taking a further 12 weeks. This work was undertaken by a team of six researchers (working mostly part-time on the project), and the research process was overseen by an Advisory Community Group. Key topics addressed included: the general drug use situation; HIV/AIDS and drugs; and harm reduction. Through the use of qualitative analysis it was found that there was: a negative moral status associated with drug use and drug users; prejudices against this group; and a lack of information about health services and HIV prevention programmes within São Vicente city. In regard to risk behavior, injecting drug users reported awareness of risks and methods of prevention. However, safer sex was considered difficult by all participants. Interventions were proposed by the research team to minimize problems and gaps in provision, and some of these have already occurred. A review of existing quantitative data found that some key institutions do not collect systematic data on drug use. Conclusions of the study include the need for interventions and the progress on Harm Reduction proposals and AIDS prevention among IDUs.