Serum sex hormone binding globulin (SHBG) was measured in 21 pre and 39 postmenopausal women with advanced breast cancer before treatment and 1, 3, 6, 9 and 12 months after ovarian irradiation or during continuous administration of tamoxifen at a dose of 10 mg twice daily, respectively; some patients received additional prednisolone at a dose of 5 mg twice a day. Ovarian irradiation was associated with a 25% reduction in serum SHBG levels 3 to 6 months after treatment whilst patients on tamoxifen experienced a rise of about 80% in serum SHBG levels after 1 to 3 months. In postmenopausal women prednisolone markedly dampened the effect of tamoxifen, reducing a 80% rise to about 20%. There was no relationship between SHBG levels and response to treatment.