Cortisol concentrations in human seminal plasma, as estimated by the very specific Amersham 'Amerlite' luminescence immunoassay, were 176 +/- 43 (85-260) nmol/l, that is, 63.7 +/- 15.5 (31-94) ng/ml (mean +/- SD, n = 21). This is about 60% of random levels in blood serum and is the first description of cortisol in seminal fluid. In human amniotic fluid at 16-22 weeks of gestation, cortisol concentrations were lower, at 72.6 +/- 14.6 (63-124) nmol/l, that is, 29.3 +/- 5.3 (23-45) ng/ml (n = 21). Concentrations were about 15% of random maternal serum levels in the second trimester of pregnancy. The cortisol concentrations in both fluids were considerably higher than those reported for saliva, which has a mean of about 10 nmol/l. Transcortin (corticosteroid binding globulin, CBG), has been found in human seminal plasma and amniotic fluid for the first time. Concentrations were low, with values up to 12 micrograms/ml, with no significant difference between the two fluids, when using the IRE-Megenix monoclonal iodinated radioimmunoassay. Transcortin concentrations were about 10% of levels in non-pregnant blood serum, compared with about 0.1% for saliva. The higher concentrations of transcortin could perhaps account for the greater diffusion of cortisol into seminal plasma and amniotic fluid. The presence of beta-endorphin, ACTH and cortisol in amniotic fluid, seminal fluid, ovarian follicular fluid, endometrial fluid and gastric fluid may possibly, indicate the existence of a small paracrine ACTH-cortisol axis in the relevant secretory tissues.