Abstract The ability of breast-carcinoma tissue to participate in steroid-hormone synthesis in vitro, led to the determination of certain steroid-hormone metabolites in urine. In particular 16-hydroxylated derivatives of dehydroepiandrosterone (D.H.E.A.) were selected since possession of a steroid 16α hydroxylase was a characteristic feature of breast-carcinoma tissue. Androst-5-ene-3β, 16α, 17β-triol (α-triol) was found to be elevated in premenopausal women with breast cancer or benign breast disease and, when expressed as a ratio to dehydroepiandrosterone or to the sum of D.H.E.A., 16α-hydroxy-D.H.E.A., and 16-oxoandrostenediol, the above group gave results highly significantly different from controls. A castrated, adrenalectomised woman with carcinoma of the breast was found to excrete D.H.E.A., 16α-hydroxy-D.H.E.A., and 16-oxoandrostenediol in her urine. After perfusion of D.H.E.A. sulphate high levels of the above compounds, together with α-triol, were found in the urine.