Bioelectrical impedance analysis (BIA) allows simple noninvasive estimation of body water, and it could potentially be a very useful technique for clinical monitoring and study of abnormalities of body water. It has been shown that the total body impedance is dominated by the arm (46%) and leg (44%). The trunk, which represents an average of 46% of the body weight, accounts for only 10% of the total impedance. The objective of the current study was to determine the errors in prediction of body composition from BIA when applied to dialysis patients with measurement on the nondominant arm, postural changes, muscular contractions or cramps, monolateral lymphoedema, arteriovenous fistula, central venous catheter, or vascular graft. We studied 20 healthy subjects, 20 uremics on chronic hemodialysis, 3 uremics with fever (body temperature >38.5 degrees C), 3 uremics with cramps, 3 patients with monolateral lymphoedema of an arm, and 3 patients with a prosthetic fistula on an arm. The results of our study show different values of total body water (TBW) derived by BIA measurements effected on supine or standing position (percentage rate variation = 1.1% to 1.6%), or effected during fever (6%), during cramps (-0.73%), with lymphoedema (25%), or in presence of a native arteriovenous fistula, a catheter in a central vein, or a graft (between -24% and +4%). We concluded that a significant error may occur in the measurement of body composition from whole body BIA when performed in the reported cases.