The bases for ethnicity-related distinctions in gonadotropin secretion are unknown, but may have important populational and physiological implications. In male contraceptive trials, exogenous testosterone and progestins suppress spermatogenesis to a greater degree in Asian than Caucasian men. In addition, iv infusion of testosterone inhibits LH release more in Asian than Caucasian volunteers. We test the converse postulate that experimental reduction of androgen-dependent negative feedback by way of the steroidogenic inhibitor combination ketoconazole/dexamethasone will unveil ethnicity-related mechanisms of regulated LH secretion in young men. LH release was monitored by sampling blood every 10 min for 24 h; immunoradiometric assay; model-free pulse detection; an entropy (regulatory) statistic; and cosine regression. Statistical comparisons revealed that healthy young Asian and Caucasian men maintain comparable baseline concentrations of LH, testosterone, estradiol, SHBG and molar testosterone/SHBG ratios. In contrast, the two ethnic groups differ prominently in each of basal, pulsatile, entropic and 24-h rhythmic LH adaptations to short-term androgen withdrawal. Therefore, we postulate that physiological nonuniformity of sex steroid-dependent negative feedback in particular may contribute to populational diversity in LH regulation.