An unusual case of CD4+helper T-cell lymphocytic leukaemia is reported in a 67-year-old Japanese woman. CD4+cells showed convoluted nuclei and dense cytoplasmic granules, features usually present in CD8+large granular lymphocytes and disorders of this particular cell type. Serum did not show antibodies to HTLV-I and HTLV-I proviral DNA integration was not evident by Southern blot analysis or after PCR. A monoclonal rearrangement of the TCR-βchain gene was evident when hybridization methods were used. The patient died 11 months after diagnosis. No skin involvement, or splenomegaly was evident. Serum LDH levels were markedly elevated but serum calcium levels were within normal limits. The case is discussed and compared to other T-cell lymphoid leukaemias. The heterogeneity in the morphology of CD4+T cell leukaemias is stressed.