Glucose tolerance tests were carried out on 35 recently discovered Indian and Black maturity-onset diabetic patients. Differences were found between the two ethnic groups although they were of comparable age, body weight, and probable duration of diabetes at the time of investigation. Glucose tolerance was worse among Blacks and was associated with low plasma insulin levels. Blacks also had lower plasma triglyceride and cholesterol values than Indian diabetics. Plasma growth hormone respone was similar in both groups. The possible role of these factors in determining the relative frequency of ischaemic heart disease in the two racial groups is discussed.