Abstract. The catecholamine producing cells of the adrenal medulla of fetal as well as adult mammals contain enkephalins. We have quantified met-enkephalin and the catecholamines, norepinephrine and epinephrine in human fetal adrenal glands during the late first trimester and throughout the second trimester of intrauterine life. Met-enkephalin (ME) was detectable in human fetal adrenals of 11 to 25 weeks' gestation by RIA. ME concentrations were low through 14 weeks (mean 279 ± 199 pg/gland), higher but extremely variable from 15 to 20 weeks (mean 1100 ± 1000 pg/gland), and then lower with somewhat less variation through 25 weeks (mean 865 ± 625 pg/gland). In contrast, catecholamine concentrations were below 1100 ng/gland through 16 weeks, then increased markedly by 21 weeks. Approximately equal concentrations of norepinephrine and epinephrine were measured throughout the gestational age period studied. Our data demonstrate that enkephalin is present in the human fetal adrenal at least by 11 weeks' gestation and suggest that the fetal adrenal may be capable of secreting enkephalins as well as catecholamines. The functional significance of adrenal enkephalin secretion remains to be elucidated.