Carraguard™ (PC-515), the Population Council's lead candidate microbicide, was tested in a triple-masked, randomized, placebo-controlled trial fielded in two sites in South Africa. The primary aims of the study were to assess Carraguard's safety (toxicity) - including signs of irritation, such as itching or burning; changes in vaginal flora; and incidence of abnormal external genital, vaginal, and cervical findings - when applied vaginally for durations of 6-12 months, and to evaluate several dimensions of the acceptability of Carraguard and placebo products. Secondary aims were to investigate whether study participants using Carraguard had lower rates of HIV seroconversion or other sexually transmitted infections (including C. trachomatis, N. gonorrhoeae, T. vaginalis, and T. pallidum) than the placebo (methyl cellulose gel). In addition, when it began, this trial was the first to explore the feasibility of large-scale microbicides testing in a non-sex worker population. Last, the trial gauged women's reactions to using a non-contraceptive product (in vitro testing had shown that Carraguard has no contraceptive effect), as well as potential use-dynamics in communities where drying agents and other traditional vaginal products are used with high frequency.