Invasive pulmonary aspergillosis is an opportunistic pneumonia which is particularly common in immuno-depressed subjects. The most frequent risk factors are the intensity and duration of leucopaenia, cytotoxic drugs and steroid therapy. In the respiratory tract, the proliferation of Aspergillus fumigatus becomes possible when there is a failure of the reticulo-endothelial system and of the polymorphonuclear leucocytes. There is no typical clinical picture: one sees an acute febrile pneumonia resistant to antibiotics. However, the radiological signs are more suggestive with nodules and bilateral infiltrates with a tendency to cavity formation and sequestration. The prognosis is clinically linked to the rapidity of diagnosis. Broncho-alveolar lavage offers a new and non-invasive diagnostic method to search for Aspergillus mycelia or specific antigens. A direct examination and culture of sputum expectoration are both insensitive and non-specific but remain useful in some patients with leukaemia in a phase of agranulocytosis. Treatment rests on Amphotericin B taken orally.