Radial bone mineral content and bone mineral density were measured in 1515 women referred for osteoporosis screening. A detailed questionnaire allowed the selection of 1069 normal white women for further analysis who had no historical evidence of bone disease or predisposing factors for bone disease. The nondominant radius was measured at two locations: the midradial bone density (MRBD) composed of predominantly cortical bone and the distal radial bone density at the 5 mm site (DRBD) composed of a mixture of cortical and trabecular bone. Women considered at risk were defined as those whose bone density values fell below fracture risk levels (0.550 g/cm2 for the MRBD and 0.325 g/cm2 for the DRBD). Between the ages of 20 and 70 years, the DRBD showed significantly greater sensitivity in defining subjects at risk (N = 223) than than MRBD (N = 80); P less than 0.001. Analysis of all ages showed that 684 women were above the fracture risk value (FRV) at both sites (64.0%), 260 were below the FRV at the DRBD 5 mm site (24.3%), 14 were below the FRV at the MRBD site (1.3%), and 111 were below the FRV at both sites (10.4%). Postmenopausal women age 50 to 70 years receiving estrogen replacement therapy (N = 221) had significantly higher values at both sites (P less than 0.001) than age-matched postmenopausal women not receiving replacement therapy (N = 239). Hereditary factors significantly correlated with both sites but neither site showed that calcium intake, activity level, or cigarette smoking were significant variables.(ABSTRACT TRUNCATED AT 250 WORDS)