The precision of total-body and regional bone mineral measurements from whole body scans obtained by dual-energy X-ray absorptiometry (DEXA) was determined in a phantom and two normal subjects. Whole body scans were performed once a week for three months at the speed of 80 mm/sec. Coefficients of variation for measurements of total-body bone mineral content (BMC) in the phantom and the subjects were 1.7% and 1.5% (average), respectively. Moreover, plots of total-body BMC values with time showed no significant slope, indicating the stability of the instrument. Regional BMC measurement from whole body scans, however, resulted in larger precision errors than total-body BMC measurement. This is attributed to the more rapid scan speed and coarser scan width used in whole body scanning as compared with regional scanning. Good precision of total-body BMC measurement by DEXA is of great clinical value in the assessment of metabolic bone disease.