We treated chronically 39 normal men with a depot androgen, testosterone enanthate (200 mg. intramuscularly), to assess its potential as a male contraceptive agent. Careful examination and quantification of testicular volume were done before, during and after several dose regimens of androgen therapy. After 4 months of weekly or bimonthly treatment with testosterone enanthate testicular volume decreased by 19.0 plus or minus 2.1 and 16.5 plus or minus 3.4 per cent, respectively. Decrease in testicular volume was related directly to decrease in sperm count. A total of 17 subjects on either weekly or bimonthly injections failed to suppress sperm counts to less than 5 million per cc after 16 weeks; testicular volume was not significantly less than control at this time. Four to 12 weeks of additional weekly injections decreased sperm counts to less than 5 million per cc in 13 of the 17 patients and decreased testicular volume by 23.0 plus or minus 4.8 per cent. The 16 additional weeks of less frequent injections (every 3 or 4 weeks) resulted in an increase in testicular volume with a return to normal size after treatment was discontinued.