This study shows that severe acne is characterized by numerous inflammatory parameters. The group of acne tetrad patients differed from those with conglobate acne in many laboratory measurements. The treatment with 13-cis-retinoic acid was well tolerated by all patients. Sebum suppression and an exfoliative cheilitis occurred in all patients, but no headache and no loss hair. Numerous previously pathological blood chemical values were normalized during the treatment. Transaminases, alkaline phosphatase, triglycerides and total cholesterol did not rise noticeably, trichological and spermatological parameters were not affected by 13-cis-retinoic acid. In an in vivo epicutaneous potassium iodide inflammation model, it was possible to demonstrate for the first time the anti-inflammatory action of 13-cis-retinoic acid.