Total body water was measured in 15 children with renal insufficiency (glomerular filtration rate < 25 ml/min per 1.73 m2) using deuterium oxide dilution. Total body water was also measured using bioelectrical impedance and skinfold anthropometry in the same 15 children. There was a linear correlation (r = 0.98, P < 0.01) between total body water measured by deuterium and height2/impedance. The 95% confidence limits for estimates of total body water were -1.5 to 0.9 for impedance and 0.65-3.16 l for skinfold anthropometry when compared with deuterium dilution. Bioelectrical impedance estimation of total body water is better than the current existing non-invasive method of skinfold anthropometry.