N uclear transfer of androgen receptors (AR) and glucocorticoid receptors (GR) was determined in cultured genital skin fibroblasts from 10 normal controls and eight patients with abnormalities of the external genitalia. In whole cell studies, cultures were incubated for 20 min at 37 degrees C with [3H]methyltrienolone (3H-R1881) or tritiated dexamethasone, and specific binding was determined in whole cell, cytoplasmic, and crude nuclear fractions. Between normal and affected fibroblasts no difference was seen in cellular levels of GR, or in cytoplasmic and nuclear distribution of GR. In normal fibroblasts, cytoplasmic binding of 3H-R1881 represented 56%, and crude nuclear binding 44%, of total binding; in fibroblasts from five of the eight patients similar values (cytoplasmic 55% and nuclear 44%) were seen for 3H-R1881 binding. In fibroblasts from the other three patients no decrease in total cellular levels of AR were seen; nuclear compartmentalization, however, was much lower (approximately 20%) than in other cultures. In vitro reconstitution studies, combining 3H-R1881-loaded cytosol with naive nuclei, lead us to suggest that the defect in nuclear compartmentalization lies at the level of the nuclear acceptor site rather than the cytoplasmic binder in affected cells. We interpret the data to suggest that defective nuclear binding of AR complexes may be involved in a proportion of cases of abnormal development of the external genitalia.