Serum from patients with warm autoimmune hemolytic anemia often contains antibodies which react with all red cell samples and interfere with compatibility testing. We describe a modification of the triple absorption procedure to absorb this "non specific" antibody reactivity from the patient's serum without decreasing the reactivity of clinically significant alloantibodies. The alloantibodies can thus be identified and compatibility testing can be performed. Red cells from selected outdated donor bloods were treated with ficin and fixed with glutaraldehyde. Samples from 79 patients whose red cells had a positive direct antiglobulin test and whose serum contained warm autoantibodies were absorbed with these cells. The results were in agreement with those obtained by warm autoabsorption or the triple absorption procedures which were used routinely in our laboratory. It was concluded that glutaraldehyde treatment of red cells does not decrease the sensitivity of the triple absorption procedure and in addition the method is practical, economical, and simple to use for personnel trained in blood bank techniques. It takes less time than standard procedures because the red cells can be prepared and stored until needed. It is particularly useful for testing sera from patients who have a low hematocrit or who have received blood transfusions in the past three months, situations in which the warm autoabsorption method may not be effective.