Forty-six subfertile men with idiopathic oligospermia were randomly assigned to 6 months of treatment with a placebo, clomiphene citrate (25 or 50 mg/day), mesterolone (100 mg/day), or pentoxifylline (1200 mg/day) or 4 months of testosterone enanthate treatment (100 or 250 mg on alternate weeks). Treatment with the placebo, mesterolone, pentoxifylline, and testosterone rebound therapy did not result in a significant increase in the mean sperm concentration or pregnancy in the partners. Clomiphene citrate at both dosages significantly increased the mean sperm concentration without improving sperm motility or morphology during the 6-month treatment period. Pregnancy rates of 36.4% and 22.2% were observed in partners of men receiving clomiphene citrate 25 mg/day and 50 mg/day, respectively. This study also illustrates the difficulties in identifying suitable patients for and assessing the efficacy of different treatment regimens.