Total body electrical conductivity (TOBEC) predictions of overall body fat were compared to combined perirenal and epididymal fat pad weights. The latter are considered to be reasonable estimates of overall adiposity. TOBEC was used to measure the body composition of 40 male Long-Evans and two male Sprague-Dawley rats ranging in weight from 210-505 g. The animals were then sacrificed and the perirenal and epididymal fat pads were removed and weighed. Core temperature was recorded before and after TOBEC values were collected. To assess the effect of position, two values were obtained for young rats: one when the tail was tucked under the rat's body and another when the tail was extended such that the full length of the measurement chamber was occupied. The TOBEC-predicted body fat was significantly different for these two positions. The best correlation between fat pad weight and TOBEC-predicted body fat (r = 0.83) was obtained when young animals were in the tail-extended position. The reliability of TOBEC readings appears to be reasonably good with mature rats.