Ninety female patients with acne were allocated randomly to one of three groups and treated either with Diane, a high dose cyproterone acetate (CPA) regime with ethinyloestradiol, or Minovlar. The same dose of oestrogen was common to all three treatment groups. Patients were assessed every 2 months for 6 months, by grading for severity of the acne, lesion counts and photography, and subjectively using a visual analogue scale. In addition, bacteriological sampling and sebum excretion rate (SER) measurements were performed. The results showed a clinical improvement in all three treatment groups, but a more rapid and complete response was seen in those groups who received CPA. There was also a consistent trend suggesting a more favourable response in those in the high dose CPA group. Although there was a marked reduction in SER in the groups treated with CPA, there was no correlation between reduction in SER and clinical improvement in individuals, nor could a reduction in the surface bacterial population be shown to be a primary event in the success of anti-androgen therapy. We have shown that the addition of CPA to oestrogen adds significantly to the therapeutic effect in acne and that anti-androgen and oestrogen combinations are more effective than standard oestrogen and progestagen contraceptive pills.