Recent interest has focused on the potential role of amylin in the pathogenesis of non-insulin-dependent diabetes mellitus (NIDDM). This 37-amino acid peptide is found in extracellular amyloid deposits in ∼50% of pancreatic islets of patients with NIDDM and has been shown to inhibit skeletal muscle glycogen synthesis in vitro. Immunocytochemical studies have colocalized amylin and insulin within β-cell secretory granules in nondiabetic humans, provoking the following questions. Is amylin cosecreted with insulin? Are circulating amylin concentrations higher in patients with NIDDM either before or after food ingestion? To answer these questions, we developed a sensitive and specific immunoassay to measure plasma concentrations of amylin in humans. Use of this assay indicated that, in lean nondiabetic subjects, glucose ingestion resulted in an increase (P < 0.001) in the plasma concentration of amylin (from 2.03 ± 0.22 to 3.78 ± 0.39 pM) and insulin (from 48.3 ± 3.1 to 265 ± 44 pM). There was a significant correlation between the concentrations of insulin and amylin (r = 0.74, P < 0.001) and the increase in insulin and amylin concentration (r = 0.65, P < 0.005). Fasting concentrations of amylin did not differ in diabetic and weight-matched nondiabetic subjects and showed a similar pattern of change after ingestion of a mixed meal. We conclude that amylin is secreted in response to ingestion of either glucose or a mixed meal and circulates at concentrations that do not differ in patients with NIDDM and nondiabetic subjects. It remains to be determined whether amylin at physiological concentrations influences carbohydrate metabolism and if so whether its effects differ in diabetic and nondiabetic humans.