The quantities of nine corticosteroids in 24 h urine samples collected by pregnant women (nine with normal foetuses and nine with anencephalic foetuses) were measured after hydrolysis with beta-glucuronidase and separation by paper chromatography. The excretion (mumol/24 h, mean +/- S.D.) of prenanetriol (0-85 +/- 0-17), 3 alpha, 17 alpha-dihydroxy-5 beta-pregnan-20-one (17 alpha-hydroxypregnanolone, 0-55 +/- 0-17), 3 alpha, 17 alpha, 21-trihydroxy-5 beta-pregnan-20-one (tetrahydro-11-deoxycortisol, 0-17 +/- 0-14) and tetrahydrocorticosterone (0-65 +/- 0-26) by women with an anencephalic foetus was significantly lower (P less than 0-01 or less than 0-05) than the excretion of these compounds by women with a normal foetus (pregnanetriol, 2-42 +/- 0-62; 17 alpha-hydroxypregnanolone, 2-72 +/- 0-69; tetrahydro-11-deoxycortisol, 0-56 +/- 0-37; tetrahydrocorticosterone, 1-95 +/- 0-94). These differences suggest that the adrenal of the normal foetus contributes to the quantity of pregnanetriol, 17alpha-hydroxypregnanolone, tetrahydro-11-deoxycortisol and tetrahydrocorticosterone in maternal urine. The excretion of tetrahydrocortisol, tetrahydrocortisone, tetrahydrodeoxycorticosterone, cortol and cortolone were similar in both groups of subjects. No evidence was obtained therefore to indicate the secretion of cortisol or deoxycorticosterone by the foetal zone of the adrenal of the undisturbed human foetus in late gestation.