There is an inherited susceptibility to polycystic ovary syndrome (PCOS). Some investigators have suggested that premature male-pattern balding is a male phenotype in PCOS families, but this remains controversial. We recently reported evidence for an autosomal monogenic abnormality in ovarian and adrenal steroidogenesis in the sisters of women with PCOS. We performed this study to determine whether we could identify a clinical or biochemical phenotype in the brothers of women with PCOS. One hundred nineteen brothers of 87 unrelated women with PCOS and 68 weight- and ethnicity-comparable unrelated control men were examined and had fasting blood samples obtained. The odds of balding (Hamilton score > or = V) did not differ in the brothers of PCOS women compared with control men. Brothers of women with PCOS had significantly elevated dehydroepiandrosterone sulfate (DHEAS) levels [brothers 3035 +/- 1132 ng/ml (mean +/- SD) vs. control men 2494 +/- 1172 ng/ml; P < 0.05]. There was a significant positive linear relationship between DHEAS levels in PCOS probands and their brothers (r = 0.35; P = 0.001). There was no significant bimodal distribution in DHEAS levels, and there were no significant differences in other parameters in brothers of PCOS women with high DHEAS levels compared with those with low DHEAS levels. There is familial clustering of elevated DHEAS levels in the brothers of women with PCOS, suggesting that this is a genetic trait. This might reflect the same underlying defect in steroidogenesis that we found in the sisters of women with PCOS. Balding was not increased in the brothers of women with PCOS. We conclude that there is a biochemical reproductive endocrine phenotype in men in PCOS families.