Using the most widely used cutoff values, 142 in 142, 140 in 140, and 90 in 93 of patients with insulinoma had end-of-fast insulin, C-peptide, and proinsulin concentrations of ≥ 3 μIU/ml (sensitivity, 100%), ≥ 0.6 ng/ml (sensitivity, 100%), and ≥ 5 pmol/l (sensitivity, 97%), respectively. The gene discussed is INS; the disease is pancreatic insulinoma.