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) in both men and women - including signs of local irritation, such as itching or burning; changes in vaginal flora (women); and incidence of abnormal external genital, vaginal (women), and cervical findings (women) - when applied vaginally prior to intercourse for 6 months; to evaluate acceptability; to gauge men's and women's reactions to a non-contraceptive microbicide; and to explore microbicide use dynamics in a Thai population.