AbstractIn the series of our studies on antilymphocyte serum (ALS) as an immunosuppressive agent in transplantation of the canine larynx, the use of ALS in thymectomized dogs was attempted for the purpose of increasing the immunosuppressive effects of ALS.Immunoglobulin G (IgG) was purified by DEAE‐cellulose batch production method from the high titer horse anti‐dog thymocyte plasma (ATP) and low titer ATP, respectively. A skin allograft assay was used to measure the immunosuppressive activity.Adult thymectomy previous to administration of the high titer‐IgG and low titer‐IgG, respectively, did not augment the immunosuppressive effect of these AT