The action of glyburide on glucose homeostasis involves pancreatic and extrapancreatic mechanisms. The relative importance of each of these processes in the hypoglycemic response to sustained administration of glyburide is unknown. In addition, the effect of this drug on the hepatic extraction of insulin is controversial. This investigation uses direct techniques in conscious normal dogs to examine the impact of glyburide therapy (2.5 mg twice daily for 4 weeks) on glucose homeostasis. Preparatory surgery included placement of Doppler flow probes on hepatic vessels and insertion of catheters in carotid artery, portal vein, hepatic vein, and renal vein. After recovery from surgery, animals underwent an intravenous glucose tolerance test ([IGTT] 0.3 g - kg (-1) intravenous glucose bolus) and an insulin infusion clamp test ([IICT] 2 mU - kg (-1) - min (-1) intravenous insulin during 150 minutes) followed by glyburide therapy. After 4 weeks, the IGTT and IICT were repeated. Glyburide increased the insulin secretory response during the late phase of the IGTT and augmented glucose clearance during the IICT. Hepatic extraction of insulin was also stimulated by glyburide. We conclude that the hypoglycemic action of long-term glyburide administration involves stimulation of both insulin secretion by the pancreas and glucose disposal by peripheral tissues. In addition, glyburide augments the extraction of insulin by the liver, and such an effect might prevent the development of sustained high levels of insulin in blood perusing peripheral tissues.