The theoretical fluid volume of 41 normal children (mean age 8 years 9 months) was estimated from anthropometric data: height, weight, wrist circumference, and body surface. The correlation between this method and the conventional methods of determining total body water using tritiated water or of extracellular fluid volume using stable bromide or bromide 82 is very good. The real fluid volumes have been measured using total body electrical impedance at low frequency (Z5 kHz) and high frequency (Z1 MHz). The correlation of these results with those obtained by anthropometry is very satisfactory (r = 0.89; p < 0,001).