Fluorescent androgen ligands were employed to study putative androgen-binding (AB) sites in a number of men with prostatic adenocarcinoma. Results were compared with biochemical androgen receptor determinations in over 150 patients with agreement in 86% (p less than 0.001). AB by histochemistry correlated significantly with the outcome of hormonal manipulation (p less than 0.001) but not with response to radiation therapy (p = 0.55) or to 125I implantation (p = 0.54). There was a degree of positive interaction between histochemically and biochemically determined AB sites which produced a significant improvement in assay specificity (p less than 0.05). These findings indicate that the best method for prediction of hormone response in prostate cancer is provided by a combination of assay techniques.