Forearm bone mineral density (BMD) was measured by single-energy photon absorptiometry in 360 healthy females without known axial fractures, 202 of whom were postmenopausal. The three sites addressed included an ultradistal (U) region containing approximately 60% trabecular bone. The other sites, distal (D) and shaft (S), were progressively more cortical. Reproducibility was 1.7-1.9% CV. The earliest evidence of a significant correlation between BMD and years since menopause was seen in trabecular bone in subjects aged 45-55 years. Fractional decrease in BMD, relative to the premenopausal value, was significantly larger at U than at S for the decades 55-65 years and above. Fractional rates of bone loss at all sites were a maximum in the first postmenopausal decade, the rate at U being 0.035, approximately 1.5 times that at D or S. A total of 33 subjects reported 54 previous minimally traumatic nonaxial (MTNA) fractures. When BMD measurements of the entire study were divided into quintiles, the prevalence of MTNA fracture cases in the lowest quintile was eight times that of each of the upper three quintiles. Prevalence of fracture cases ranked by quintiles of BMD were not different for the three scan sites. Therefore, ultradistal measurements confer no advantages over distal or shaft BMD for discriminating past MTNA fracture cases but do show larger fractional rates of loss during the first postmenopausal decade.(ABSTRACT TRUNCATED AT 250 WORDS)