Blood glucose profiles, fasting blood glucose and glycated haemoglobin were followed prospectively for 6 weeks in 14 patients with non-insulin-dependent diabetes (NIDDM). Capillary blood glucose was sampled weekly on filter paper and analysed in the laboratory. Glycated haemoglobin was determined every other week with both cation-exchange chromatography (HbA1-IEC) and aminophenylboronic acid affinity chromatography (GHb-PBA). The mean for the blood glucose profiles was 11.2 +/- 3.5 mmol l-1 (+/- SD) and the mean for fasting blood glucose was 9.5 +/- 2.8 mmol l-1. For individual patients the differences between mean fasting blood glucose and mean blood glucose varied from -1.3 to 4.2 mmol l-1. There was a linear relationship between blood glucose and glycated haemoglobin which was steeper for GHb-PBA than for HbA1-IEC. The correlations with fasting blood glucose and mean blood glucose for HbA1-IEC were r = 0.85 and r = 0.92 and for GHb-PBA r = 0.87 and r = 0.96 respectively. Mean blood glucose was better correlated to glycated haemoglobin than fasting blood glucose (p < 0.05 for GHb-PBA).