The main objectives of this study were to investigate changes in the vulvar, vaginal, and cervical epithelia, the vaginal flora, and HIV-1 shedding in the genital tract of female participants, and changes of the penile skin and epithelia of male participants. We also evaluated symptoms reported by participants, and several dimensions of the acceptability of and compliance with the study or placebo gel. Reactions to a non-contraceptive microbicide were assessed, as well as reasons for voluntary discontinuation and non-use of Carraguard® or the placebo (determined by review of daily diary) was recorded. Exit focus group discussions were held with male and female participants to discuss aspects of acceptability and compliance. Self-reported symptoms were also investigated by clinical examination as needed and study endpoints included genital itching or burning, frequent urination, burning while urinating, genital pain, pain during sex, and abnormal vaginal or penile discharge.