Antilymphocyte sera (ALS) vary considerably in both immunosuppressive capacity and toxicity. We have developed an assay which will predict the immunosuppressive capacity of different preparations of ALS. 11 is based on the in vivo mode of action of ALS and measures the ability of ALS to alter the localization of injected MCr-labeled thymus cells. In addition, we have described an assay which will reflect the potential toxicity of batches of ALS. These assays are applicable to both antimouse and antidog lymphocytc sera and will enable the selection of immunosuppressive yet nontoxic preparations of ALS. © 1969 S. Karger AG, Basel.
