Direct Coombs tests were performed in 265 patients with solid tumors, leu-kemias and malignant lymphomas. The frequency of highly positive Coombs tests varied from 5.52 in the solid tumors (13 % for the carcinomas) to 52 % in chronic lymphotic leukemia. A secondary autoimmune hemolytic anemia, without antibody, was present in 2 cases of solid tumors and in one case of Hodgkin's disease. A dubious or slightly positive Coombs test was frequently observed without signs of increased hemolysis. On the other hand, a strongly positive Coombs test was associated with an acute hemolysis in most cases but in patients with macroglobulinemia. Biological tests usually considered as characteristic for secondary hemolytic anemia (reticulocytosis, unconjugated bilirubin, urinary excretion of urobilinogen, serum iron, granulopoiesis/erythropoiesis ratio) have not an unequivocal significance : they may be normal in cases with true hemolytic anemia or abnormal in patients with a normal survival time of the red cells. The presence of more than 2 abnormal tests is however indicative for the diagnosis of hemolytic anemia, especially if there is no liver deficiency.