We have used a simple and rapid method for the determination of total fast hemoglobins (HbA1a+b+c) in 102 diabetics and 36 normal controls. The method was described by Kynoch and marketed by Isolab. It proved to be useful in screening for patients with inadequate metabolic control in whom as a rule, total fast Hb values were higher than 8.5%. Mean Hb A1a+b+c value was significantly higher in the group of diabetics in comparison with normals (9.9 +/- 0.2 versus 6.9 +/- 0.8%). The diabetic patients were separated into four groups according to predetermined criteria of recent metabolic control. Even the patients considered to have a very good diabetes control during the past eight weeks, had supranormal total fast Hb values (7.7 +/- 0.2%). In the patients with good, poor and bad diabetes control, mean total fast Hb levels were respectively 9.3 +/- 0.3, 10.1 +/- 0.3 and 12.5 +/- 0.4%. In normals, there was a positive correlation between individual fasting blood glucose and total fast Hb values and in diabetics, mean blood glucose values correlated with total fast Hb levels. Hb A1a+b+c determinations also correlated with triglyceride values. We could find no significant association between high total fast Hb levels (greater than 8.5%) and the prevalence of retinopathy.