Androgen receptor content was correlated with various prognostic factors in 274 patients with breast cancer. Receptor content was determined by the dextran-coated charcoal method (DCC). No direct relationship was found between androgen receptor content and age of patient, menstruation status, TN status and number of affected lymph nodes. But in 232 patients in whom tumour differentiation could be determined, there was a highly significant relationship between it and androgen receptor content (P less than 0.01). Similar correlations were found also between these prognostic factors and oestrogen or progesterone receptors. The percentage distribution of tumours of different degrees of differentiation was independent of the kind of demonstrable steroid-hormone receptor. However, the frequency of highly differentiated tumours rose with the number of different receptors that were determined. Thus steroid-hormone receptors can be considered as markers for differentiation. It seems possible that the additional determination of androgen receptors allows for a more exact selection of patients who should receive hormonal treatment.