A 24-year-old Japanese woman was admitted to our hospital in 1987 with a chief complaint of skin eruptions, and was diagnosed as having chronic ATLL. In 1993 the leucocyte count increased gradually to 126.0 x 10(9)/l with 91.5% abnormal lymphocytes expressing two different types of antigenicity, either CD+/CD8- or CD4-/CD8+. Monoclonal integration of human T-cell lymphotropic virus type-I proviral DNA was detected at different sites of the genomic DNA in each cell type. These studies clearly indicate that CD4+/CD8- and CD4-/CD8+ leukaemic cells originated from two independent clones.