In 4 of 6 normal subjects, the intravenous injections of 0.03 mg of glucagon/kg body weight, 2.5 hours after the in-gestion of a standard fat breakfast caused a reduction of serum tri-glyceride concentration either toward or to the postabsorptive levels within 1/2 hour. Of the 2 exceptions, one failed to display any rise in concentration of triglycerides following the fat meal, prior to glucagon injection and the other failed to have a hyperglycemic response to glucagon. The rise in concentration of his serum triglycerides could be prevented by glucagon only when he was fed additional glucose with the fat meal. Concentration of nonesterified fatty acids, measured in the sera of 2 subjects decreased following glucagon administration. The effect of glucagon on serum lipids is secondary to its hyperglycemic effect.