Patients with type 2 diabetes mellitus are usually treated initially with oral antidiabetic agents, but as the disease progresses, most patients eventually require insulin to maintain glucose control. Optimal insulin therapy should mimic the normal physiologic secretion of insulin and minimize the risk of hypoglycemia. This article discusses the role of insulin therapy in patients with type 2 diabetes, emphasizing long-acting insulin agents designed to approximate physiologic basal insulin secretion and provide control over fasting plasma glucose. Clinical trials of recently developed long-acting insulins are reviewed herein, with emphasis on studies that combined basal insulin with oral agents or with short-acting insulins in a basal-bolus approach. The normal physiologic pattern of insulin secretion by pancreatic beta cells consists of a sustained basal insulin level throughout the day, superimposed after meals by relatively large bursts of insulin that slowly decay over 2 to 3 hours (bolus insulin). Basal support with long-acting insulin is a key component of basal-bolus therapy for patients with diabetes who require insulin with or without the addition of oral agents. Newer long-acting agents such as insulin glargine provide a steadier and more reliable level of basal insulin coverage and may have significant advantages over traditional long-acting insulins as part of a basal-bolus treatment strategy.