Fundamental studies on the ability of a newly developed 90-detector dual energy X-ray absorptiometry (DEXA) system with a fan beam, the DCS-3000, to determine bone mineral density (BMD) were performed. This new system not only measured BMD precisely, resulting in a fast scan mode in CV of 0.89% and 1.63% for in vitro and in vivo studies, respectively, but also performed data acquisition in a greatly reduced examination time (24 sec). Furthermore, when a rod phantom was used, the linear regression equation obtained between BMD quantified with the QDR-1000 (x) and that quantified with the DCS-3000 (y) was y = 1.250x-0.242. In both healthy subjects and osteoporotic patients, significant positive correlations were obtained between radial BMD and vertebral BMD measured with the QDR-1000 and with the DCS-3000. The correlation for radial BMD was r = 0.533 (p less than 0.001, N = 76), and that for vertebral BMD was r = 0.985 (p less than 0.001, N = 56). Therefore, in addition to safety of operation, the performance of the DCS-3000 was considered to be equal to that of commercially available DEXA systems, indicating that it should be useful in the detection of vertebral bone loss.