Carraguard™ (PC-515), the Population Council's lead candidate microbicide, was tested in a triple-masked, randomized, placebo-controlled trial fielded in one site in Chiang Rai, northern Thailand. The primary aims of the study were to assess Carraguard's safety (toxicity) - including signs of local irritation, such as itching or burning; changes in vaginal flora; and incidence of abnormal external genital, vaginal, and cervical findings - when applied vaginally for 12 months; to evaluate acceptability; to assess feasibility of conducting a large scale microbicide trial in a non-sex worker population; to gauge women's reactions to a non-contraceptive microbicide; and to explore microbicide use dynamics in a Thai population.