Hemoglobin A1c concentrations were measured in 107 out patients with non insulin treated diabetes. A good correlation was observed between Hb A1c and random post-prandial plasma glucose levels. Mean Hb A1c concentrations were slightly higher in these diabetics than in controls but markedly lower than values observed in insulin treated patients. Sixty three per cent of the patients had Hb a1c levels below three standard deviations above our normal mean value. Random post-prandial plasma insulin levels were correlated to the degree of overweight but not other parameters. The best results were observed in patients treated by diet alone (31 % of the whole population) and in those on diet and sulfonylureas (30 %) who were also the less older and the less overweight subjects.