The effects of chronic (2 weeks) hyperinsulinemia on the production of very low density lipoprotein (VLDL) triglyceride and on VLDL particle size were examined. Hyperinsulinemia was induced by a constant sc infusion of 6 U porcine insulin/day from an osmotic minipump. To avoid profound hypoglycemia, these rats received chow plus 10% sucrose in their drinking water. Therefore, two control groups were examined; one receiving chow plus the same amount of sucrose (high carbohydrate control) and the other receiving chow only (chow control). The constant infusion model was compared to a previously reported model of hyperinsulinemia. In that model, NPH insulin was injected for 2 weeks twice daily in incrementally increasing doses (final dose, 6 U/day) into rats that were also fed chow and given 10% sucrose drinking water. Results with the injection model were similar to those previously reported: an increase in triglyceride production in face of a decrease in FFA, a minimal decrease in serum triglyceride, and some decrease in serum glucose. The infusion model produced the same increase in triglyceride production and decrease in fatty acid concentration. However, it differed in producing an increase in serum triglyceride and no change in serum glucose. The former suggested that in the infusion model triglyceride removal was not stimulated as much as in the injection model. Since there was no hypoglycemia in the infusion model, it was unlikely that VLDL changes were caused by an increase in counter regulatory hormones. VLDL particle size was increased in the high carbohydrate controls. This indicated that changes in sucrose supplementation led to the production of more triglyceride-filled VLDL particles. Hyperinsulinemia was not accompanied by any further increase in particle size. Thus, the hyperinsulinemia-induced increase in VLDL-triglyceride production was accompanied by an equivalent increase in VLDL particle production.