This study reports lipid studies on dogs up to 44 weeks following portacaval shunt. We have shown portacaval shunt to be associated with significant decreases in plasma cholesterol and triglyceride levels in the dog. Cholesterol synthesis and absorption appear to be unchanged following operation when compared to control animals. Two-hour postprandial serum bile acids are fortyfold greater in shunted animals than in control dogs. Further studies of the interrelationship of bile acid and cholesterol metabolism following portacaval shunt are suggested.