Leukaemic infiltration of the lungs may occur in acute myeloid leukaemia (AML). Pulmonary infiltrates are usually microscopic and invariably associated with hyperleucocytosis. Four AML patients with respiratory symptoms and low leucocyte counts underwent standard chest radiography, bronchoscopy with bronchoalveolar lavage and high-resolution computerized tomography (HRCT) of the lungs. HRCT scans showed pulmonary infiltrates with alveolar, interstitial, mixed and peribronchial/perivascular patterns in all patients, including one with negative standard radiographic findings. Infectious agents were excluded. Histology of the lung biopsy/autopsy specimens showed leukaemic infiltrates. Pulmonary leukaemia may be the cause of pulmonary infiltrates, even in non-hyperleucocytosic AML patients with low blast counts.