We compared two bioelectrical impedance analysis models, the right-sided tetrapolar method and an experimental cylindrical method, to total body water (TBW) determined by isotopic dilution in 37 prepubertal children aged 5-9 years, who were divided into development and cross-validation groups. Despite its theoretical advantage, no improvement in predicted TBW was seen with the experimental method. The best predictive equation, using the tetrapolar method, was TBW (kg) = 1.84 + 0.45 (height square/resistance) +0.11(weight); r2 = 0.98; SEE = 0.62 kg.