The present report describes a method for125I anti‐IgG antiglobulin testing. The method involves the use of a labeled DEAE cellulose IgG fraction of goat anti‐human IgG globulin. Leukocyte‐free red blood cells were used in the test procedure. Both the labeled antiserum and the red blood cell suspensions were diluted in normal rabbit serum to prevent nonspecific uptake of labeled antiserum by normal, un‐coated red blood cells.The results of the study show that the method is highly reproducible and relatively easy to perform once the labeled anti‐IgG is prepared. Furthermore, the use of labeled antiserum permits analysis of antiserum specificity by radioimmunoelectrophoresis. The problem of determining anti‐IgG/IgG binding ratios remains the major disadvantage to using the method to determine precise amounts of human IgG coating red