This study was carried out to assess the sensitivity of single photon bone absorptiometry (SPBA) as an early screening tool for osteoporosis and select the optimum site for measurement. We measured bone mineral density (BMD) at the distal tenth of both radius and ulna (D-BMD) and at the ultradistal radius, a site distal to the point at which the radius and ulna are 8 mm apart (UD-BMD). Our study group consisted of 107 healthy women aged 25-60 years (mean +/- SD: 45.8 +/- 10.0), subdivided according to age into 3 groups: Group 1: 25-40 years, Group 2: 41-50 years, Group 3: 51-60 years. When comparison was made to Group 1, D-BMD was found significantly reduced only in Group 3 (p < 0.0001), while UD-BMD was found reduced in both Groups 2 (p < 0.02) and 3 (p < 0.0001). The percent reduction of BMD in Groups 2 and 3 with respect to Group 1 was significantly greater at the ultradistal site than at the distal tenth of the radius and ulna (p < 0.0001 versus D-BMD). Despite limits inherent in the cross-sectional study design, our results suggest that forearm SPBA indicates post-menopausal bone loss irrespective of scanning site, but detects pre-menopausal loss sensitively only at the ultradistal site. Ultradistal measurement would therefore seem suitable for early screening for osteoporosis as an alternative or in addition to the generally used more proximal site.