Steroid profiles of urinary 17-oxosteroids, pregnanediol and pregnanetriol were studied by gas-liquid chromatography in normal Japanese and British women, and in women with breast cancer from both races. The results showed that both pre- and post-menopausal Japanese women excreted significantly less aetiocholanolone, 11-oxo aetiocholanolone, and 11-hydroxy aetiocholanolone than their British counterparts. Androsterone was significantly less in Japanese pre-menopausal women and pregnanetriol in post-menopausal women respectively. However, a significantly lower androsterone ( 5α): aetiocholanolone ( 5β) ratio was found in the Japanese cancer patients than in the normal Japanese women (pre-menopausal, P = < 0.02, post-menopausal, P = < 0.05). In the British pre-menopausal breast cancer patients this 5α: 5β ratio was higher than in the normal British control (P = < 0.02). A comparison of blood plasma TSH levels with the urinary androsterone: aetiocholanolone ratios gave a significantly negative correlation in both the Japanese normal and cancer cases (P = < 0.05). No agreement was found in a similar comparison in the British women. These results could signify that a diminished thyroid function may be a predisposing factor to breast cancer in Japanese women.