Nuclear binding of androgen was examined, using R 1881, a synthetic androgen. The amount of androgen-receptor complexes bound to isolated nuclei was determined in isolated adipocytes from the epididymal (Epi), retroperitoneal (Ret), inguinal (Ing) and mesenteric (Mes) adipose tissues from intact and castrated rats. The binding was specific and saturable with a Kd in the nanomolar range. Binding was examined after 2 days and after 1 and 2 weeks after castration, showing a higher binding in the Mes tissue in comparison with Ing at all time-points (P < 0.05). Mes adipocytes showed a trend (0.05 < P < 0.1) to up-regulate their binding capacity 2 days after castration, and a significant (P < 0.05) downregulation 2 weeks after castration. Two days after castration, R 1881 binding, expressed per mg triacylglycerol (TG), was generally higher in the Mes region (P < 0.05). This was not fully significant in comparison with Epi tissue in intact rats. When expressed per cell the differences were somewhat diminished, due to differences in cell sizes. Androgen binding showed a negative correlation with TG-uptake in vivo (r = 0.85, P < 0.01), suggesting that a higher density of androgen receptors leads to a more inhibited lipid uptake. In conclusion, a specific androgen receptor was demonstrated in adipose tissue in rat, showing regional differences and a negative correlation with the lipid accumulation of the tissue.