Fasting serum lipoproteins were measured in patients with carcinoma of the prostate. Twelve patients were on no hormonal treatment (Group 1). Fifteen were on cyproterone acetate (Group 3), 17 were on the long-acting LHRH analogue Zoladex (Group 4) and 11 on a combination of cyproterone acetate and Zoladex (group 5). In addition, 27 patients with benign urological disease were taken as controls (Group 2). In both groups in which cyproterone acetate was part of the treatment the total high density lipoprotein cholesterol levels were significantly lower than in the other groups. Patients on cyproterone acetate alone had significantly higher levels of very low density lipoprotein (VLDL) triglyceride levels than those not on cyproterone acetate. These results confirm changes in serum lipoprotein levels in patients taking cyproterone acetate and these changes may have potential adverse effects if the treatment is prolonged.