Abstract: Measurements of total-body bone and soft tissue were compared between two fan-beam dual-energy X-ray absorptiometry (DXA) scanners, a Hologic QDR 4500A, a Lunar Expert, and a pencil-beam Hologic QDR 1000W. Phantom studies showed that mass measurements were not compromised by magnification effects, but that the height of a bone within the body affected the measured bone mineral content (BMC) and, to a lesser extent, the bone mineral density (BMD). There were differences in calibration for fat proportion between the three instruments. Comparisons on volunteers demonstrated very high correlations of bone and soft tissue measurements, but regression coefficients differed from unity, and intercepts were significant. With all three scanners, wrapping lard around the limbs of a volunteer, to simulate weight change, changed the apparent BMC and BMD.