The nuclear androgen receptor (ARn) content of cancerous prostatic tissue has been investigated as a prognosticator for time to progression under endocrine therapy. In 1981 a prospective study was started to investigate whether the ARn content in biopsy specimens of patients with prostatic carcinoma predicts the duration of response following hormonal treatment. ARn was estimated by a microassay which involves extraction of nuclear pellets with a heparin-containing buffer, exchange labeling of the nuclear extract with 3H-R1881, and quantitation of the receptor with protamine sulphate precipitation. One hundred and fifteen patients with prostatic cancer entered this study; 47 patients had evidence of metastatic disease as proven by bone scan. Forty-two patients were treated by orchiectomy; 37 of these patients are evaluable with a minimal follow-up of 30 months. A relationship between the nuclear androgen receptor content and the time to progression following orchiectomy in these patients with metastatic disease of the prostate was not found. This could possibly be attributed to the heterogeneous nature of the prostatic tumor tissue with respect to the distribution of the ARn. We conclude that androgen receptor assay in needle biopsies, at least in this study, had no value for the prediction of the time to progression after orchiectomy.