A study was carried out to evaluate the effectiveness of glipizide in insulin-dependent diabetic patients. An intravenous glipizide (2 mg) test was carried out in 7 patients before and after a period of associated insulin-glipizide treatment (mean daily dose of 80.7 i.v. lente insulin and 14.3 mg glipizide for 9.1 months) to assess the capacity of the sulphonylurea to reduce acutely the plasma glucose and lactate levels. Glipizide did not produce glucose variations in either test but did result in a significant decrease, in the first test only, in mean plasma baseline levels of lactate, which were higher than normal in these patients. There was no reduction in daily insulin requirements after the period of associated glipizide-insulin treatment. It is concluded that, in the dosage used, intravenous glipizide probably has no hypoglycaemic effects in insulin-dependent diabetics. Moreover, it did not prove useful in combination with insulin. However, the reduction in plasma lactate may be related to an acute enhancement of the exogenously administered insulin. This improvement in the insulin effect may be an acute one among the so called "extra-pancreatic" actions which have been demonstrated for glipizide and other sulphonylureas.