Changes in body composition are found in chronic uraemia, but it is unclear if this results from poor nutrient intake or is a consequence of impaired renal function. To investigate this question, 31 female Wistar rats were allocated to undergo subtotal nephrectomy or sham operation and were fed diets of either 24% casein or 24% soya protein. Three months later measurements of inulin clearance were undertaken in the conscious animal and the carcass subsequently analyzed for body water and body fat. Subtotally nephrectomized animals had a significantly greater proportion of body water (p < 0.001) and a lesser proportion of body fat (p < 0.001) than control animals, and a significant correlation was found between glomerular filtration rate and body fat content (24% casein diet: r = 0.96; 24% soya diet: r = 0.71). The dietary protein source appeared not to influence the body composition. These results support the concept that altered body composition in uraemia is due to renal dysfunction rather than altered nutrient intake.