Background and Objectives: The AIDS epidemic has brought barrier contraceptives to the forefront of public health research. A comprehensive evaluation of the efficacy of barrier contraceptive use in preventing sexually transmitted diseases (STDs), including AIDS, is necessary to inform both potential users and public health policy makers. This study was undertaken to evaluate the efficacy of condoms and vaginal spermicide products, used alone or in combination, in preventing gonorrhea and chlamydia among women attending an STD clinic. Goal of this Study: To describe the general characteristics of the study group and its follow-up experience. Study Design: Women who met the eligibility criteria were invited to participate. The initial visit included an interview, a behavioral intervention promoting barrier methods, a physical examination, and instructions to complete a sexual diary. Participants received free barrier contraceptives and returned for six monthly follow-up visits. Design Results: Participants (n = 1,122) were low income, single (74%) black (89%) women with a median age of 24. The behavioral intervention led to the use of barrier protection in more than 70% of reported acts of vaginal intercourse. Barriers were used consistently (100% of sexual acts) during 51% of the months of follow-up. A total of 148 cases of gonorrhea (28 per 1,000 months) and 122 cases of chlamydia infection (23 cases per 1,000 months) were diagnosed during follow-up. Conclusion: This study represents a practical solution to a complex set of design considerations. The study protocol was successful in promoting consistent and proper use of barrier methods.