Androgens and estrogens interact in neural tissues to regulate behavioral and neuroendocrine responses. As an initial attempt to identify the cellular level at which these steroids interact, we characterized the time course of nuclear androgen receptor (ARn) occupation in the preoptic area of the hypothalamus (POA) after chronic dihydrotestosterone (DHT) administration and determined whether it was modified by concurrent treatment with estradiol benzoate (EB). We found that ARn levels peaked (47.1 +/- 12.6 fmol/mg DNA) by 12 h after castrated rats were treated with Silastic capsules filled with crystalline DHT and remained significantly elevated for at least an additional 12 h. When EB was injected (2 micrograms/rat) at the same time the DHT capsules were inserted, peak levels of ARn in POA were reached sooner (6 h) and retained longer (48 h). Comparisons with other central and peripheral tissues suggested that this response was unique to the POA. These results suggest that estrogens may modify the response of POA neurons to androgens by altering the duration of ARn occupation.