During an 8-hour perfusion of isolated rat liver the following phenomena were studied: kinetic blood levels of glucose, urea and potassium, activity of glutamic-oxalacetic and glutamic-pyruvic transaminases and alkaline phosphatase, hemolysis, bile production and endohepatic blood pressure. The effects of sterile and non-sterile conditions of perfusion, dialysis and infusion of nicotinic acid on these parameters were observed. A simple and versatile apparatus for long-term liver perfusion of small laboratory animals is described.