Through forming a collaborative relationship to develop, pilot and evaluate an innovative bio-psycho-behavioral (BPB) HIV prevention intervention, capacity was built in developing an effective intervention and conducting community based research at both the California Prostitutes Prevention and Education Project (CAL-PEP) and the University of California's Family Health Outcomes Project. The research objective was to investigate whether the BPB intervention that included sexually transmitted diseases (STD) testing and behavioral counseling, is superior to standard HIV counseling and testing. This necessitated building capacity at CAL-PEP to deliver clinical services, implement the counseling model, conduct outreach and follow-up, and manage data. University of California, San Francisco, staff needed to build capacity to listen to and incorporate feedback from staff with widely diverse educational and cultural backgrounds. The outcome was to develop the study questionnaire and effective follow-up systems as well as to be able to teach research methods to these staff. Frequent staff meetings to promote trust and mutual respect, incorporating staff and client input into the intervention design, and ongoing training and quality assurance processes were critical to the project's success. Preliminary analyses indicate the BPB intervention is effective at improving condom related attitudes, self-efficacy to use condoms, and intentions to practice other HIV/STD risk reduction.