Analysis of the aggregation of erythrocytes as measured by aggregation index in blood samples obtained from patients with elevated levels of immunoglobulin G (Ig G) and immunoglobulin A (Ig A) is carried out. The aggregation index (AI) and plasma viscosity (PV) are correlated with the total protein, albumin, Ig G, Ig A and Ig M and total globulin concentrations of samples and are compared with that of normal blood. The results show that the AI depends more on the monoclonal globulin concentrations and this dependence is more for Ig A than that for Ig G. There is no correlation between either AI and IgM in both these samples. The present study shows that the aggregation index could further be used as a rapid supplementary test for the initial investigation and therapeutic response of hyperglobulinemic patients. © 2001 Éditions scientifiques et médicales Elsevier SAS.