Androgen receptors were measured in soluble and nuclear fractions of tissues obtained from 25 patients. A method using mibolerone, a synthetic androgen, as a ligand is described. This method, which includes the presence of excess ORG 2058 to eliminate interaction with progesterone receptors, gives a reliable determination of androgen receptor content and has been used to predict response to hormonal treatment. However, the results suggest that the presence of functional receptor is not, in itself, a sufficient index of hormonal dependence of the tumour.