Although oral glucose tolerance test (OGTT) has been the key examination in early diagnosis of diabetes mellitus, but it still has some problems. It may be affected by some physiological or pathological changes and also requires frequent blood sampling. We investigated the usefulness of measuring the level of glycated hemoglobin (GHb) or HbA1 and HbA1c in screening or early diagnosis of diabetes mellitus. OGTT was performed and fasting levels of HbA1 and HbA1c were measured in 168 subjects. According to the diagnostic criteria of WHO for 75g OGTT, 31 subjects were classified as normal, 35 as having impaired glucose tolerance test (IGT) and 102 as diabetics. The method used for determination of HbA1 and HbA1c was high pressure liquid chromatography (HPLC). The total discovery rate for GHb in diabetic patients was 87%. In patients with fasting level of plasma glucose (FPG) greater than or equal to 8 mmol/L the discovery rate was 100%, while in those with level of FPG less than or equal to 7.94 mmol/L the rate was 80%. Thus, GHb is very useful in screening and early diagnosis of NIDDM (type II), especially diabetes mellitus of the elderly.