This study consists on an eight week completely randomized investigator blind trial designed to compare the relative efficacy and tolerance of clindamycin phosphate topical solution and tetracycline in the treatment of patients with mild to moderate acne vulgaris. Patients were seen at baseline, weeks 2, 4, 6 and 8. Of the forty-five case report forms received in house, thirty-four are considered to be evaluable. Seven patients failed the entry criteria, two patients were lost to follow-up and two patients left due to lack of tolerance to the medication. All patients receiving medication were examined for both local and global tolerance indices. Within group analyses show significant improvement for both medication groups with respect to the continuous efficacy parameters: inflammatory lesions, pustules, papules and comedo counts. After adjusting for initial baseline differences, no differences between the two groups arose for these variables. The investigating physician on the average judged clindamycin phosphate to be significantly more efficacious than tetracycline trends for the patients evaluation supported these results. Throughout the study, the incidence of peeling, erythema and itching was low and similar for both groups. Two tetracycline patients did however terminate participation in the study due to itching. Significantly more patients receiving tetracycline complained of a burning sensation. No diarrhea or other side effects were recorded.