To evaluate the clinical usefulness of measurements of glycated haemoglobin in the assessment of metabolic regulation in non-insulin-dependent diabetes mellitus (NIDDM) in primary health care, measurements of glycated haemoglobin, HbA1c, were compared with postprandial blood glucose measurements. 120 consecutive patients with NIDDM, following the routine control by their general practitioners, were offered a measurement of HbA1c. Approximately two-thirds of the patients bad HbA1c values above the acceptable level, despite postprandial blood glucose values withii the recommended intervals of good and acceptable metabolic control. Blood glucose values above 10.0 mmol/l, indicating poor metabolic regulation, were reflected in high HbA., values. Measurements of HbA1c provide an index of metabolic regulation over time, which is otherwise not obtainable in the usual clinical setting, and HbA1c should be measured regularly to evaluate long-term metabolic control and the need for intensified therapy in patients with NIDDM.