A case of autoimmunohemolytic anemia following mefenamic acid therapy is described. A free anti-erythrocytic antibody of the IgG class was found in the serum of the patient. The same antibody was also found in the eluate of the patient's red cells. No blood group specificity could be demonstrated. Direct participation of the drug in the antibody red cell reaction could be ruled out by "facilitation" and "inhibition" tests.