AbstractAlthough these studies do not allow a definitive differentiation between the relative influence of chemotherapy and radiotherapy on mitogen‐induced lymphocyte transformation, the data suggested both radiotherapy and chemotherapy can cause depression; however, radiotherapy may have a more pronounced effect. The relationship between the absolute peripheral blood lymphocyte count and phytohemagglutin and pokeweed mitogen‐induced lymphocyte transformation was also analyzed. These data revealed that patients who are receiving or who have received intensive therapy may have normal peripheral absolute lymphocyte counts with impaired lymphocyte transformation. Serial studies of lymphocyte transformation were evaluated in 10 children with acute lymphoblastic leukemia who received both chemotherapy and radiother