A 55-year-old man was treated during 22 months with chlorambucil (total dose : 4 218 g) for glomerulonephritis. Towards the end of the treatment, he developed acute myelomonocytic leukaemia and died of this complication. The authors underline the oncogenetic dangers of the association dysimmune disease/immunosuppressive treatment and draw attention to the almost regular preleukaemic phase with its well-known cytological, biochemical, immunological, cytogenetic and evolutive criteria.