Glycohemoglobin (GHb) levels were assayed after chromatography on weakly acidic acrylic cationite columns in 167 patients undergoing glucose tolerance test (GTT) and in 105 known diabetics. In 95% of patients with normal GTT levels, the GHb level was in the range of 6.8% to 9.8%. The GHb level was normal in patients with latent diabetes. Glycohemoglobin levels were elevated in patients with poorly controlled diabetes. Even in patients with normal GTT results, GHb levels correlated positively with fasting plasma glucose and glucose tolerance values. In patients with abnormal GTT results or diabetes but not receiving insulin therapy, the correlation between GHb levels and fasting plasma glucose values was significant. The GHb level that distinguished between latent and overt diabetes correlated strongly with the values of fasting plasma glucose and glucose tolerance and reflected changes in the control of diabetes.