Whole cerebral and cerebellar flow (CBF and Cb1BF) measurements with single-photon emission computed tomography were performed on 14 postmenopausal women 4 weeks after the discontinuation of hormone replacement therapy. After the first brain blood flow measurements, nine subjects received 0.625 mg of conjugated equine estrogens (CEE) orally twice a day continually for 3 weeks (study group). The remaining five did not receive CEE (control group). The second brain blood flow measurements were performed on all 14 subjects between 2 and 3 weeks after the first ones. The mean whole CBF value (&OV0335; ±; SE) in the study group was significantly increased from 45.9 ±;3.4 to 58.8 ±; 5.5 ml/100 g/min during estrogen replacement therapy (ERT) (p = 0.0382). The mean whole Cb1BF value was also significantly increased from 47.7 ±; 3.4 to 61.0 ±; 5.6/100 g/min during ERT (p = 0.0382). In the control group, there were no significant differences between the first and second flow measurements either in the mean whole CBF values (46.6 ±; 2.5 versus 44.6 ±; 5.4 ml/100 g/min) or in the mean whole Cb1BF values (46.3 ±; 2.2 versus 44.2 ±; 5.2 ml/100 g/min). The mean percent changes were 29.5 ±; 10.2% in CBF and 29.3 ±; 10.4% in Cb1BF. These results suggest that ERT significantly increases the whole cerebral and cerebellar blood flows in postmenopausal women.