1. No significant difference in serum high-density-lipoprotein (HDL) cholesterol was observed when control rats were compared with rats with streptozotocin-induced diabetes of 14 days duration. Blood glucose and serum cholesterol and triglyceride concentrations were significantly higher in the diabetic group.
2. In a second experiment rats with streptozotocin-induced diabetes of 8 days duration were given long-acting porcine insulin (1 unit/day or 3 units/day subcutaneously for 14 days) and were compared with a control group. Blood glucose and serum cholesterol and triglyceride concentrations did not differ significantly with the two doses of insulin and there was no significant difference between serum high-density-lipoprotein cholesterol in control rats and either of the two groups of rats given insulin.
3. When the rats given insulin were grouped according to their blood glucose concentrations, those with blood glucose in the range 20–30 mmol/l were found to have significantly higher serum high-density-lipoprotein cholesterol concentrations than those with higher or lower blood glucose levels or than controls. There was thus a statistically significant curvilinear relationship between blood glucose and serum high-density-lipoprotein cholesterol concentrations.