Chlorpropamide present in concentrations of 50 or 100 mg./1OO ml reduces glucose output by isolated rat livers perfused with Tyrode''s solution. The release of amino acid N was increased by chlorpropamide in livers perfused with glucose-free Tyrode''s solution but was decreased when both chlorpropamide and glucose were present in the perfusing fluid. Chlorpropamide was without effect on urea production by the isolated perfused liver.