The effect of acute uremia on stores of pancreatic insulin was examined. Four groups of rats were studied: nephrectomized rats on a special low nitrogen diet, sham-nephrectomized rats on the same diet, sham-nephrectomized rats on a normal diet, and normal rats on a normal diet. Uremia created by nephrectomy was allowed to continue for 6 days at which time animals were sacrificed. A period of 10 days of diet equilibration was done prior to nephrectomy. Total body weight, pancreas and liver weights declined in sham-operated and nephrectomized rats mostly attributable to the diet. In uremic rats, however, heart weights increased. Insulin expressed as U/g pancreas, total insulin per animal, U/100 g body weight, or as per cent of protein was significantly depressed in the uremic rats compared to sham-operated special diet controls.