PIP: More than a dozen different candidate HIV/AIDS vaccines have been tested and well-tolerated in uninfected human volunteers in small studies. International health agencies are therefore moving ahead to plan field efficacy trials. Scientists agree that field trials must be randomized, placebo controlled, and double-blinded. Further, trials must be conducted in populations with HIV incidence rates in the range of 1-3 new infections/100 persons/year. Given this rate of infection, 3000-5000 at risk volunteers would be needed. The need for only voluntary participation and risk-reduction education among volunteers are also considered.