Monocyte recognition of immunoprotein-coated erythrocytes in vitro was studied in 21 patients with immune hemolytic anemia. Simultaneous assessment of immunoglobulin and complement components on the patients' erythrocytes was performed. The patients were heterogeneous in relation to associated diseases, therapy, and duration of disease state; 15 were studied within 1 mo of diagnosis and 4 additional patients were studied in sequential fashion. Monocyte-erythrocyte interaction was assessed by both a morphologic and a radioactive assay; 12 of 17 patients had elevated ratios in the morphologic assay and 15 of 17 patients had elevated ratios in the radioactive assay. The majority of patients exhibited enhanced interaction between their monocytes and autologous immunoprotein-coated erythrocytes, as compared to normal moncytes exposed to the same immunoprotein-coated erythrocytes. These findings suggest that there is an enhanced capacity of monocytes from certain patients with immune hemolysis to interact with autologous immunoprotein-coated erythrocytes in vitro.