The study presents clinical data and results of skin sebum (SER) determinations during 13-cis-retinoic acid treatment in 15 patients suffering from severe conglobate and cystic acne. The striking clinical improvement was mostly accompanied by decreased SER as well as changes in the composition of the skin surface lipids. While the sebaceous gland lipids were generally reduced, the epidermal lipids showed irregular tendencies. Despite of good therapy effects, 3 patients showed increased SER. This indicates that other mechanisms than those of sebum suppression may be responsible for the treatment success. Sebum suppression and modulation are important and valuable aspects for documentation as well as for elucidation of the working mechanism of 13-cis-retinoic acid.