Dual-energy X-ray absorptiometry (DXA) measures three of the principal components of the body: fat mass, lean soft-tissue mass (comprising muscle, inner organs, and the body water), and the bone mineral content. The purpose of this study was to test the estimation capacity of DXA when it is applied to patients with end-stage renal failure. Twenty dialysis patients were examined by DXA before and after one hemodialysis session. A highly significant positive correlation between weight measurements performed by conventional scales and DXA was found. A positive correlation between fluid loss during dialysis and reduction in fat-free mass (lean soft-tissue mass plus bone mineral content) was observed by DXA. The estimation of the fat-free mass was independent of the amount of fluid loss. No significant differences in variance between the data obtained before and after the dialysis were observed. We conclude that DXA is a useful tool for estimating the magnitude of body compartments in patients with end-stage renal failure.