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This study evaluated a commercially available bioelectrical im­pedance instrument as a tool for the assessment of body composition. Deter­mination of whole-body resistance (R) was made, using a tetrapolar electrode arrangement, on 188 men and women ranging from 18 to 64 years of age. Total body water (TBW) was assessed by deuterium oxide dilution procedures and ranged from 22 to 57 1. Body density and lean body mass (LBM) were determined by underwater weighing; the lean body mass values ranged from 28 to 82 kg. Whole-body resistance (R) demonstrated moderate but significant inverse relationships with LBM and TBW (r = —0.68 and — 0.65, respectively). There were high correlations between stature (S) and LBM and TBW (r = 0.85 and 0.83) and between weight (W) and LBM and TBW (r = 0.83 and 0.84). Similarly, significantly high correlations (r = 0.93 and 0.83) were observed between LBM and resistance predicted lean mass (LBM-r) and TBW and resistance predicted total body water (TBW- r), respectively. Paired t-tests indicated that significant differences existed between LBM and LBM-r and TBW and TBW-r, implying the manufactur­er’s equations should be modified. Multiple regression analysis was used to develop prediction equations for LBM-r and TBW-r, with males coded as 0 and females coded as 1.LBM-r = 17.7868 + 0.000985*S2 (cm) + 0.3736*W (kg) - 0.0238*R (ohm) - 4.2921*SEX - 0.1531‘AGE (yrs)R2 = 0.917 SEE = 3.231 KgTBW-r = 9.9868 + 0.000723‘S2 (cm) + 0.2822*W (kg) - 0.0153*R (ohm) - 2.3313*SEX - 0.1319*AGE (yrs)R2 = 0.871 SEE = 2.919 L