We studied the effects of zinc deficiency on hepatic androgen metabolism and aromatization, androgen and estrogen receptor binding, and circulating levels of reproductive hormones in freely fed, pair-fed and zinc deficient rats. Hepatic conversion of testosterone to dihydrotestosterone was significantly less, but formation of estradiol from testosterone was significantly greater in rats fed the zinc-deficient diet compared with freely fed and pair-fed control rats. There were significantly lower serum concentrations of luteinizing hormone, estradiol and testosterone in rats fed the zinc-deficient diet. No difference in the concentration of serum follicle-stimulating hormone was observed between the zinc-deficient group and either control group. Scatchard analyses of the receptor binding data showed a significantly higher level of estrogen receptor in zinc-deficient rats (36.6 +/- 3.4 fmol/mg protein) than in pair-fed controls (23.3 +/- 2.2 fmol/mg protein) and a significantly lower level of androgen binding sites in rats fed the zinc-deficient diet (6.7 +/- 0.7 fmol/mg protein) than in pair-fed control rats (11.3 +/- 1.2 fmol/mg protein). There were no differences in hepatic androgen and estrogen receptor levels between freely fed and pair-fed controls. These findings indicate that zinc deficiency reduces circulating luteinizing hormone and testosterone concentrations, alters hepatic steroid metabolism, and modifies sex steroid hormone receptor levels, thereby contributing to the pathogenesis of male reproductive dysfunction.