In this study we compared the effects of high-dose and low-dose testosterone enanthate (TE) administered with the same dose of cyproterone acetate (CPA). Eighteen men aged 21-45 were treated with CPA 5 mg/day and with TE 100 mg/week (n = 9; CPA-5-100) or TE 200 mg/week (n = 9; CPA-5-200) for 16 weeks. Semen analyses were performed every 2 weeks; physical examination and chemistry, hematology, gonadotropin, and testosterone measurements were performed every 4 weeks. At week 16 of treatment, sperm counts were significantly more suppressed in the CPA-5-100 group than in the CPA-5-200 group. Sperm counts returned to baseline in all subjects after hormone administration ceased. No difference in gonadotropin levels was found at any time between the 2 groups. During the treatment phase, testosterone levels were significantly higher in the CPA-5-200 group than in the CPA-5-100 group. The present study confirms that CPA/TE administration induces profound sperm suppression. An increase in the dose of androgen resulted in less profound sperm suppression despite no difference in gonadotropin suppression. These data suggest that high testosterone levels can maintain sperm production in men.