1. The seasonal variation of fasting blood glucose, peroral glucose tolerance, fasting plasma insulin and triglycerides and the sum of insulin values during glucose tolerance test was studied in 100 patients who had suffered a myocardial infarction. These patients comprised a population of all men who had suffered a myocardial infarction below the age of 55 years and had survived.
2. The material was divided into four numerically equal groups covering two dark, cold periods and two warm, light periods of the year.
3. Lower fasting blood glucose and insulin values during glucose tolerance test as well as a trend to higher glucose tolerance were found during the warm, light part of the year in comparison with winter. Triglycerides and fasting insulin values did not vary significantly in these infarction patients. The variation could not be explained by a difference in age or body weight between the groups.
4. It is suggested that glucose tolerance and insulin secretion are subjected to seasonal variation in man as has previously been shown in laboratory animals.