Specific progesterone-binding protein (P4-BP) is demonstrated in adrenocortical nuclei of the guinea pig, but, not in nuclei of other animals. We tried to demonstrate the progesterone-binding activity in nuclei of human normal adrenals and adrenal tumors. Normal adrenals were obtained from six patients with renal cell carcinomas undergoing radical nephrectomy. Seven adrenocortical adenomas were obtained: five tumors from patients with Cushing's syndrome, one tumor from non-functioning adenoma, and one from aldosteronoma. Nuclei were purified from the tissues, and progesterone binding assay was performed. We could not demonstrated progesterone-binding activity in nuclei of six normal human adrenals. However, we demonstrated progesterone-binding activity in nuclei purified from human adrenocortical adenomas associated with Cushing's syndrome. Saturation analysis revealed a Kd of 13.85 +/- 1.99 nM (mean +/- SD, n = 5) and a binding capacity of 1.95 +/- 0.37 pmol/mg DNA (mean +/- SD, n = 5). A Kd of progesterone-binding activity in human adrenocortical adenoma was similar to that of guinea pig P4-BP, and a binding capacity was about one-fifteenth of guinea pig P4-BP. However, nuclei purified from a non-functioning adrenocortical adenoma and an aldosteronoma failed to demonstrate progesterone-binding activity. The binding activity was specific for progesterone. 5 alpha-pregnane-3,20-dione was a modest competitor, while 17 beta-estradiol, testosterone, cortisol, and other related steroids were poor competitors. Thus the progesterone-binding activity in human adrenals was similar to guinea pig P4-BP in the affinity and specificity of binding.(ABSTRACT TRUNCATED AT 250 WORDS)