The mean glycosylated haemoglobin A1 level in 200 diabetics, 13.2%+/-2.6 (1SD), was nearly twice the level found in 100 non-diabetics, 7.42%+/-0.6 (1SD), and overlap between the two populations was minimal. Glycosylated haemoglobin A1 levels, fasting and two hour post-prandial blood glucose concentrations and 24 hour urinary glucose excretion were measured at intervals over a period of 12 weeks in six diabetics requiring stabilisation. A close correlation was found between glycosylated haemoglobin A1 levels and short term parameters of control.