We determined fructosamine concentrations with the CentrifiChem 600 centrifugal analyzer and the Hitachi 737 discrete analyzer. Reference intervals agreed with the most recently published results, and values in fasting patients were significantly correlated with glycated hemoglobin, plasma glucose, albumin, beta- and gamma-globulins, IgG, IgA, IgM, and total protein. Partial correlation analysis showed that only fructosamine and IgA were dependently related. In a group of nondiabetic patients with pathological values for IgA concentrations, 79.4% had pathological values for fructosamine. These results throw doubt on the clinical value of fructosamine determinations if serum IgA is not taken into account.