A 31 year-old male who was treated with radiation under the diagnosis of malignant lymphoma was admitted to our hospital because of systemic erythema and tumor of bilateral upper arms in October, 1987. Leucocyte count of peripheral blood showed 4,400/microliters with 36% leukemic cells and bone marrow was hypercellular with 85.6% leukemic cells. Leukemic cells were negative for peroxidase reaction and lineage specific monoclonal antibodies such as CD3, CD4, CD8, CD10, CD19 and CD20. T cell receptor (TCR) delta gene was rearranged but TCR beta, TCR gamma and immunoglobulin (Ig) genes were in germline configuration. He was treated with combination regimen of doxorubicin, vindesine, prednisolone and L-asparaginase, and complete remission was obtained. These observations suggest that TCR delta gene rearrangement is useful for determination of clonality in cases without rearrangements of the other TCR and Ig genes.