To elucidate the role of early insulin response in postprandial hyperlipidemia, we examined triglyceride (TG) and remnant-like particle triglyceride (RLP-TG) levels, using a meal tolerance test (MTT) with or without the administration of nateglinide (NAT). The MTTs were performed 2 d apart in 36 drug-naive patients with type 2 diabetes who had been hospitalized for glycemic control while receiving diet therapy. Before the second MTT, patients were treated with 90 mg NAT. Treatment with NAT was associated with a significant increase in insulin levels in the treated patients 1 h after the test meal, compared to levels in non-treatment. NAT treatment was also associated with a significant decrease in the level of free fatty acids 1 and 2 h after the meal, and with a significant decrease in plasma glucose levels 1, 2, and 4 h after the meal, compared to those in non-treatment. During the first MTT with NAT non-treatment, 13 patients showed serum TG levels of 200 mg/dL or greater when measured 2 h after the meal. In these 13 patients, NAT administration produced a significant decrease in TG levels 1, 2, and 6 h after the meal, as well as a significant reduction in RLP-TG levels 1 and 2 h after the meal. NAT administration was also associated with significant reductions in area under the curve (ΔAUC) for TG and RLP-TG. These results suggest that, in a clinical setting, the early insulin response is closely associated with both postprandial glucose and postprandial lipid metabolism in Japanese patients with type 2 diabetes.