Acne is a mutlifactorial disease of the pilosebaceous follicles of the face and upper trunk in which the microorganism,Propionibacterium acnes, is thought to play a central role in the initiation of inflammation.P. acnesis a member of the resident cutaneous microflora and is found in similar numbers on the skin surface and in the pilosebaceous ducts of nonacne subjects, so the disease should not be regarded as an infection. A number of theories have been proposed to explain the role of the organism in the pathogenesis of acne, but conclusive evidence to substantiate any of them is still lacking. However, agents that inhibit the growth of cutaneous propionibacteria are therapeutic, and topical and oral antibiotics remain the most frequently prescribed treatment for acne. More severe cases virtually always respond to therapy with 13-cisretinoic acid. This drug prevents the recurrence of acne in two thirds of patients, but the remaining patients need repeated courses or maintenance on alternative therapies. The highlight of the year under review has been the discovery of bioactive interleukin-1α in the majority of open comedones. The observation that one third of 500 antibiotic-treated acne patients seen in a major dermatology outpatient clinic during 1991 harbor drug-resistant propionibacteria is a cause for concern.