Children and young adults (N = 52, age 7-31, average 15.3 years) from parents with or without a history of onset of diabetes mellitus after the age of 30 years were studied for anthropometric and metabolic parameters related to diabetes. An oral glucose tolerance test was performed and blood samples were collected fasting and 15, 30, and 60 minutes after a standard glucose load. Offspring of diabetic parents were significantly heavier and more obese, although not uniformly overweight. Blood pressure, fasting insulin, glucagon, and triglycerides were significantly higher in offspring of diabetic parents. Approximately one-half of the offspring and siblings of diabetic parents had 30-minute blood glucose levels greater than 161 mg/dL, whereas none of the controls exceeded this level. These observations suggest abnormalities consistent with diabetes mellitus are already present in children and young adults, and may be detected by a response to glucose load.