In a randomized, controlled double-blind study involving 139 patients with various forms of acne, the effectiveness and tolerance of Saccharomyces cerevisiae Hansen CBS 5926 (Perenterol) was studied in comparison with a placebo over a maximum period of five months. The results of therapy were assessed by the physician as very good/good in 74.3% of the patients receiving the preparation, as compared with 21.7% in the placebo group. In more than 80% of the former patients, the condition was considered to be healed or considerably improved, while the corresponding figure for the placebo group was only 26%. Seasonal differences in the effect of treatment with Saccharomyces cerevisiae Hansen CBS 5926 were not observed. Side effects leading to a premature discontinuation of the test were seen neither in the test substance group nor in that receiving placebo. The therapeutic efficacy of Saccharomyces cerevisiae Hansen CBS 5926 makes this systemic form of therapy an alternative that is becoming more and more widely accepted by acne patients.