1. In 126 normotriglyceridaemic and in seventy-three hypertriglyceridaemic subjects there was a similar seasonal variation of adipose tissue lipoprotein lipase activity, the lowest activity being noted during the summer months.
2. There was no seasonal variation of the serum triglyceride or free fatty acid concentrations in the normotriglyceridaemic group.
3. In the same group the highest blood acetoacetate concentration was noted in March–April, the lowest in November–December.
4. There was no seasonal variation of the blood glucose concentration for women, but for men the lowest concentration was noted in July–August.