The interpretation that L-asparaginase is a selective inhibitor directed only against neoplastic tissues, particularly lymphoid neoplastic tissue, does not seem to be entirely true. In fact: 1.1. Schreck [1] showed that not only leukemic but also normal lymphocytes in culture are damaged if L-asparaginase is added to the medium. 1.2. Broome [2] observed that the content of free asparagine quickly diminishes in the thymus and in the spleen of the C3H mice treated with L-asparaginase. 1.3. It appeared that some rapidly growing tissues are impaired by L-asparaginase. This effect was observed in rabbit embryos and fetuses (Adamson and Fabro [3]), and in the liver of partially hepatectomized rats (Becker and Broome [4], Grundmann [5]), as well as in the proliferation kinetics of human bone marrow in culture (Boll and Reckers [6]). Also the growth of HeLa cells in culture became highly inhibited by EC-2 asparaginase (Oerkermann and Hirschmann [7]). 1.4. Astaldi, Burgio et al. [8] showed that E. coli L-asparaginase intensely inhibits blastic transformation of human peripheral blood lymphocytes in the PHA-culture system. 1.5. McElwain and Hayward [9] were then able to show the same effect also when the enzyme is administered i. v., and the lymphocytes are subsequently removed and cultivated in the PHA-medium. KeywordsMaximum ExtentHuman Peripheral Blood LymphocyteMixed Lymphocyte CultureMitogen PokeweedBlastic TransformationThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.