Vaginal tolerance tests were performed with a new potential microbicidal and spermicidal product, an acid-buffering vaginal gel (Acidform) without or with nonoxynol-9 (N-9). The potential advantages over other vaginal products include keeping a low pH, decrease of the irritating effect of N-9 on the cervix or vaginal mucosa associated with greater retention of the product after application, and decreasing "messiness" as compared to other vaginal products. Three groups of six women were admitted and randomly assigned to use Acidform with 0%, 2.5%, and 5% N-9. Colposcopic evaluation for vulvar, vaginal, and cervical signs of irritation was performed and photographs were taken, following a specific World Health Organization protocol, at time 0, and after 24 h and 6 days of application of the gel. No irritation or symptom was reported by users of Acidform without N-9. A generalized and intense erythema in cervix was observed in 10 of 12 Acidform/N-9 users and abrasion occurred in nine of them. Vulvar irritation was seen in seven of these 10 volunteers. N-9 concentration in the gel (2.5% or 5.0%) was not related to the findings. No ulcer, exulceration, or de-epithelialization was observed. Acidform without N-9 was well tolerated by volunteers, but it was unable to protect the cervix, vagina, and vulva from the N-9 effects.