Morning versus bedtime administration of NPH insulin was compared in 12 subjects with Type 2 diabetes and overt fasting hyperglycaemia. Subjects were studied at baseline (diet alone) and after 2 months on each of the two insulin programmes in a random crossover design, in which dosage was increased until at least one daily preprandial blood glucose was consistently in the range of 3.9 to 6.0 mmol l-1. Mean (+/- SEM) daily total insulin dosage was equivalent for the morning (0.36 +/- 0.03 units kg-1) and for the bedtime (0.37 +/- 0.03 units kg-1) insulin administration schedules. Glycaemic control was improved on both insulin regimens, but was better on bedtime than morning insulin. Fasting plasma glucose (mmol l-1) was 12.0 +/- 0.7 (baseline), 8.6 +/- 0.7 (morning), and 4.6 +/- 0.3 (bedtime), respectively. Mean 24 h plasma glucose (mmol l-1) was 13.3 +/- 1.3, 9.0 +/- 0.7, and 7.8 +/- 0.7. Glycated haemoglobin (%) was 7.65 +/- 0.35, 6.23 +/- 0.26, and 5.81 +/- 0.32. The improvement of basal glycaemia is a consequence of increased basal metabolic clearance of glucose (baseline, 47.6 +/- 3.1 ml m-2 min-1; morning 63.5 +/- 5.4, bedtime 103.5 +/- 7.1). There was no change in hepatic glucose output. It is concluded that bedtime administration of intermediate acting insulin results in increased basal insulinaemia, leading to improved basal glycaemia and consequent improved overall metabolic control, compared to morning insulin administration. Therefore, bedtime may be the preferable timing of insulin therapy for patients with Type 2 diabetes and overt fasting hyperglycaemia.