Oestrogenic influence of the non-steroidal anti-oestrogen tamoxifen may have consequences for the morbidity pattern among women on long-term adjuvant treatment. Subclinical oestrogenic effects of adjuvant tamoxifen on the tissue level was studied among 16 postmenopausal women in three different organ systems: the pituitary, the liver and bone. After 3 months of adjuvant tamoxifen prolactin levels decreased 66% (P < 0.001) in comparison with pretreatment levels. There was an 80% increase in basal growth hormone after 3 months of treatment in comparison with pretreatment levels, which did not reach statistical significance (P = 0.07). Sex hormone binding globulin levels increased 39% (P < 0.01) and IGF-1 (somatomedin C) levels decreased 20% (P < 0.05). The levels of bone GLA protein (BGP; osteocalcin), a marker of bone osteoblastic activity, decreased 28% (P < 0.01). In 13 of the patients bone mineral density (BMD) was measured before treatment and after 1 year. No significant change in BMD was observed. The results thus suggest a clear oestrogenic effect of tamoxifen on the pituitary, liver and bone in postmenopausal women.