Disruption of the insulin receptor substrate-2 was shown to cause type 2 diabetes in mice. This could be largely attributed to abnormalβ -cell development. In humans, a prevalent polymorphism in insulin receptor substrate-2 (Gly1057Asp) was not found be associated with type 2 diabetes in linkage and association studies. We tested the hypothesis that an extreme challenge of the β cell might reveal subtle abnormalities in carriers of this polymorphism undetected by conventional insulin secretion tests. Therefore, in addition to assessing β-cell function by oral glucose tolerance testing (n = 318, normal glucose tolerance), we measured the secretory response to maximal stimulation by hyperglycemia (10 mm), glucagon-like peptide-1, and arginine administered in an additive fashion (n = 77, nondiabetic). The allelic frequency of the Asp allele was ∼37%. Neither the β-cell function indices from the oral glucose tolerance test nor the secretory response during the hyperglycemic clamp differed measurably between carriers and controls. Moreover, maximal plasma C-peptide concentrations in response to the combined glucose, glucagon-like peptide-1, and arginine stimulus was not different between Gly/Gly (10,745 ± 1,186 pmol/liter) and X/Asp (10,800 ± 490 pmol/liter, P = 0.99). In conclusion, our findings strongly suggest that the Gly1057Asp polymorphism in insulin receptor substrate-2 is not associated withβ -cell dysfunction. The normal maximal insulin secretory response makes it unlikely that this common polymorphism results in abnormalβ -cell development.