The effects of acute uremic syndrome on serum glucose, insulin, triglycerides and cholesterol were studied in the fasted rat 24 h following bilateral nephrectomy. The mean levels of serum glucose and immunoreactive insulin (IRI) as well as insulin to glucose ratio were significantly higher in the uremic animals than in the shamoperated controls. The fasting hyperglycemia in the presence of high levels of circulating IRI observed in the nephrectomized rats reflects a decrease in the efficiency of insulin-mediated glucose transport. The acutely anephric rat develops both significant hypertriglyceridemia and hypercholesterolemia, accompanied by a prominent increase in all lipoprotein classes. The generalized nature of the hyperlipoproteinemia as well as the lack of any positive correlation between serum lipids and circulating IRI or insulin to glucose ratio suggest that the observed hyperlipidemia must be attributed to factors other than hyperinsulinemia or insulin insensitivity alone.