A patient is described, having Richter's syndrome and immunodeficiency with hyper IgM, who developed suppressor T cell lymphoma (CD3+, CD4-, CD8+) following untreated helper-suppressor T cell chronic lymphocytic leukemia (CD3+, CD4+, CD8+). The neoplastic T cells in both malignancies expressed interleukin (IL) 2 receptors but were deficient in typical CD2+ and CD5+ pan T antigens. Additionally, a large percentage of malignant lymph node T cells expressed HLA-DR+ activation antigens. In vitro immunoglobulin-production experiments demonstrated that the patient's leukemic blood T cells had an excess helper function for IgM synthesis but a suppressor function for IgG and IgA synthesis by normal B and T cells. The leukemic blood T cells demonstrated a poor response to phytohemagglutinin (PHA). A defect in IL 2 receptor expression was evident in PHA-stimulated leukemic blood T cells. Of interest was the observation that PHA stimulated the induction of a novel CD3+, CD4-, CD8+ T cell subset from patient's CD3+, CD4+, CD8+ leukemic blood T cells. These PHA-induced CD3+, CD4-, CD8+ T cell subsets produced an elevated proliferative response to PHA and concanavalin A, had a helper cell function for IgM synthesis and produced highly elevated amounts of IL 2.