Preliminary clinical studies (2) proved the effectiveness of topical azelaic acid (AZA) in the treatment of acne vulgaris. During the period of 1982-86 we carried out two studies with 20% AZA cream in patients with acne to determine its clinical indications and therapeutic schedules. The first, open study was of 100 unselected patients of either sex, while a second group of 30 patients formed a part of a larger (309 patients) multicentre single-blind comparison of topical AZA vs. 5% benzoylperoxide (BPO) gel for the treatment of papulopustular acne. The rates of improvement obtained indicate that topical AZA can be considered an effective therapy chiefly for papulo-pustular acne, with a very good local tolerance.