1. Infusion of a triglyceride emulsion (Intralipid) into overnight fasted normal subjects produced a rise in plasma free fatty acids (FFA) and blood ketones.
2. Glucose given orally 60 min after the start of the Intralipid infusion produced a sharp fall in blood ketones without much change in plasma FFA.
3. An infusion of glucagon given together with Intralipid did not alter the reduction in blood ketones produced by oral glucose in normal subjects.
4. Oral glucose given 60 min after the start of the Intralipid infusion in three insulin-requiring diabetic subjects produced no fall in blood ketones.
5. The results suggest that glucose prevents the increase in blood ketones after Intralipid through an increase in insulin secretion rather than through a suppression of glucagon or as a direct effect of glucose.
6. It is most likely that the effect of insulin is to inhibit hepatic ketogenesis.