Invasive aspergillosis is a disease of the immunosuppressed patient. We describe two patients with acute lymphoblastic leukaemia who attained complete remission, with partial or complete bone marrow recovery, but who went on to develop fatal invasive aspergillosis contemporaneous with recovery of neutrophil counts. Quantitative recovery of peripheral blood neutrophil counts does not guarantee control of Aspergillus infection, perhaps due to functional neutrophil deficiencies post-chemotherapy, and specific defensive strategies adopted by the organism itself.