Infections caused by fungi of the genus Aspergillus have become a major and dangerous problem in the modern treatments of blood diseases using cytotoxic drugs. Invasive pulmonary aspergillosis, generally caused by A. fumigans and A. flavius, is the usual clinical manifestation of the disease, but subacute forms have been described in patients with little immunodeficiency. The clinical signs, not very suggestive, are those of an infective pneumonia, and localized radiological forms are initially more frequent in most cases. Diagnosis rests on pathological data, but in many cases the only possible examinations are broncho-alveolar lavage and bronchial brushing which give both sensitive and specific results. Treatment is basically medical and consists of intravenous infusions of amphotericin B. The earlier the treatment the better the outcome which seems to be more favourable in patients with localized infection.