We describe a method for estimating hemoglobin A1c (HbA1c) with a commercially available enzyme immunoassay system. The method is based on microtiter plate technology, utilizing an antibody raised to hemoglobin, the epitope being the Amadori product of glucose plus the first eight amino acids on the N-terminal end of the beta chain of hemoglobin. The enzyme immunoassay displays good within-batch (CV 2.3-2.4%) and between-batch (CV 2.6-5.0%) precision, and the results were not affected by different types of anticoagulant. The method was linear within the expected range of results and showed good correlation (r = 0.88-0.98) with established methods for estimating glycohemoglobin. Using this method, we obtained a reference interval of 2.8-4.9% (central 95%) for HbA1c in a nondiabetic population. The percentages of hemoglobin that were HbA1c in diabetics (6.86% +/- 2.51%) were significantly greater (P < 0.001) than in nondiabetics (3.46% +/- 0.52%).