Summary A multicentre, randomized double‐blind study was performed to assess the effect on male fertility of treatment with low dose clomiphene citrate. One hundred and ninety couples were included in whom the male diagnosis was idiopathic impairment of semen quality, and the female partner had no demonstrable abnormality or was under successful treatment for a minor endocrine problem. A total of 1308 couple‐months were studied. Men received either 25 mg clomiphene citrate daily or placebo for 6 months. The cumulative life‐table pregnancy rates at 8 months were 11.7% and 8.1% in the placebo and clomiphene groups respectively. There were no significant differences between the changes in semen quality during intake of either clomiphene or placebo. This study provides no evidence for the efficacy of clomiphene citrate for the treatment of idiopathic male infertility.