The enzyme-linked antiglobulin test (ELAT) was employed to measure the number of IgG molecules per red blood cell (IgG/RBC) in 11 patients with autoimmune hemolytic anemia (AIHA). All patients with AIHA had high levels of red cell-associated IgG (110-3, 650 IgG/RBC). The control group consisted of normal volunteers (N = 10) and patients with hereditary spherocytosis (N = 1), beta 0-thalassemia (N = 1), immunologic thrombocytopenic purpura (N = 3) and IgG multiple myeloma (N = 4). All control individuals presented low levels of red cell IgG (less than 38 IgG/RBC) with the exception of one of four patients with myeloma who had a mildly elevated value (50 IgG/RBC). Since the multiple myeloma patients had greater than 2 g/dl IgG, the possible nonspecific uptake of IgG onto the RBCs of patients with elevated serum IgG values did not interfere with the results of ELAT. ELAT proved to be a useful method for accurate quantification of the amount of IgG specifically bound on the surface of RBC of patients with AIHA.