The objective of this study was to compare the effect of two sulphonylureas on the frequency of hypoglycaemic events and glycaemic control in elderly patients with Type 2 diabetes. Twenty-two untreated elderly patients were treated with glibenclamide or gliclazide in a randomized double-blind fashion. Prior to treatment, a biochemical profile, an oral glucose tolerance test, and a 2-h hyperglycaemic glucose clamp (glucose 5.4 mmol l-zs-1 above baseline) were performed. Patients were seen regularly over 6 months to assess glycaemic control and the frequency of hypoglycaemic reactions. Hyperglycaemic clamp studies and oral glucose tolerance tests were repeated at 1 and 6 months. The area under the curve for the oral glucose tolerance test (glibenclamide: 15.5 +/- 0.7; gliclazide: 14.9 +/- 0.8 mmol l-1 (p = NS)) and the haemoglobin A1C (glibenclamide: 7.4 +/- 0.2%; gliclazide: 7.9 +/- 0.5% (p = NS)) were similar at 6 months. Hypoglycaemic reactions were significantly more frequent with glibenclamide than with gliclazide: 17 vs 4 (p < 0.01). Insulin sensitivity index (ml kg-1 min-1 pmol-1 x 100) was increased significantly by glibenclamide but not gliclazide (glibenclamide: 0.284 +/- 0.116 (baseline) vs 0.518 +/- 0.102 (6 months) (p < 0.05), gliclazide: 0.260 +/- 0.048 (baseline) vs 0.358 +/- 0.048 (6 months) (p = NS)). We conclude that glycaemic control was equivalent with the two drugs but the incidence of hypoglycaemic reactions was significantly greater with glibenclamide probably because this drug increases insulin sensitivity to a greater degree.