Exposure to elemental mercury (Hg) vapour results in an accumulation of Hg in the pituitary, the thyroid, and the testis. In this study, basal serum concentrations of pituitary hormones (thyrotrophin (TSH), prolactin (PRL), follicle stimulating hormone (FSH), and luteinising hormone (LH] or their response after administration of thyrotrophin and gonadotrophin releasing hormones did not differ between 11 male workers (mean urinary Hg (U Hg) concentration 26 nmol/mmol creatinine) and nine male dentists (U Hg concentration 1.3 nmol/mmol creatinine) exposed to elemental Hg vapour when compared with matched referent groups (U Hg concentration 0.6 and 0.4 nmol/mmol creatinine). Thus there was no evidence of an effect of Hg on the pituitary. Neither was there any association between exposure to Hg and serum concentrations of free thyroid hormones (S FT3, S FT4), testosterone, or cortisol. Increased plasma concentrations of selenium (Se) were associated with increased basal serum concentrations of TSH, decreased concentrations of basal serum cortisol, and decreased release of FSH.