We have evaluated radial bone mass and sex steroid concentrations in a group of postmenopausal white type 2 diabetics, that group at greatest risk of developing osteoporosis. The linear regression of midshaft bone mass on age for 79 patients showed a rate of loss about half the rate for normals. These data suggest that bone is lost at a slower rate by this group, and the difference cannot be explained by obesity or glucose control alone. A subset of 40 of these subjects was chosen for further study. As expected, these women had significantly higher bone mass than normals; in addition, they were significantly heavier (82.4 +/- 2.7 kg v 65.3 +/- 1.8 kg, P less than .001), and had higher body mass index (32.1 +/- 1.0 kg/m2 v 25.2 +/- 0.6 kg/m2, P less than .001), than controls. Serum estrone concentrations were higher (49.8 +/- 3.7 pg/mL v 28.5 +/- 1.8 pg/mL, P less than .001); serum androstenedione (0.28 +/- 0.03 ng/mL v 0.51 +/- 0.04 ng/mL, P less than .001), and serum testosterone (0.18 +/- 0.02 ng/mL v 0.26 +/- 0.02 ng/mL, P less than .02) concentrations were lower among diabetics than controls. Serum estradiol (15.1 +/- 1.7 pg/mL v 15.3 +/- 1.0 pg/mL, P greater than .5) was not significantly different. Multiple regression analysis indicates that the excess level of estrone concentration among diabetics increased with the degree of obesity. The explanation for the lower concentration of the other sex steroids among diabetics is not known.