We report a case of a T-zone malignant lymphoma of a cervical lymph node developing in a 25-year-old man. Only 14% of the marrow was originally involved, but within two months massive, leukemic dissemination ensued. The blast cells were unable to bind sheep erythrocytes (E) but expressed human thymus leukemia antigen (HTLA) and common ALL-stem-cell (cALL) antigen and had high terminal deoxynucleotidyl transferase (TdT) and acid phosphatase activity. These findings suggest a malignant lymphoproliferative disorder of pre-T-cell type. Complete remission was achieved with intensive chemotherapy. Two months later, acute myelomonocytic leukemia was diagnosed; at this time, over 90% of the blast cells were peroxidase, sudan black, and chloracetate-esterase positive. Consistent with loss of high TdT activity and HTLA and cALL antigens, 86% of the blasts now expressed Ia-like antigens. Cytogenetic studies demonstrated hyperdiploidy. Reports of granulocytic leukemia in lymphoma are reviewed in the context of the above findings and the hypothesis that a leukemogenic factor affects a multipotential stem cell.