This brief review encapsulates a nearly 50-year career in biomedical research, primarily studying human leukemias and lymphomas, but also involving normal lymphocytes. Early observations included the feasibility of bone marrow transplantation (and related problems with graft-vs.-host reactions); the mitogenic effect of phytohemagglutinin (and resultant human lymphocyte culture techniques); and early cytogenetic findings in human leukemias, both lymphocytic and myeloid (including the Philadelphia chromosome). Subsequent studies of normal human lymphocytes have contributed to our enormously expanding knowledge of their basic biology, especially regulatory pathways, both extracellular and intracellular. Further work with human lymphoid neoplasms has helped extend the early chromosomal findings to the specific genes involved, including several regulating apoptosis; and also contributed to the concept of clonal evolution as a basic underlying mechanism of tumorigenesis in general. This career has covered a period of remarkable growth of knowledge concerning both normal and neoplastic lymphocytes, with potential for many important future clinical applications; it has been a privilege to participate.