Quantification of haemosiderin-laden macrophages in bronchoalveolar lavage fluid (BALF) has been used to diagnose diffuse alveolar haemorrhage (DAH) but has not been assessed in patients with diffuse alveolar damage (DAD). The present study analysed BALF obtained from 21 patients with DAD diagnosed by surgical lung biopsy. The median age of 21 patients with DAD was 68 yrs (range 18-79 yrs); 14 (67%) were male and 12 (57%) were immunocompromised. The median proportion of haemosiderin-laden macrophages in BALF was 5% (range 0-90%), but was >or=20% in seven (33%) patients, fulfilling the commonly used BALF criterion for DAH. There was a trend toward a positive correlation between the percentage of haemosiderin-laden macrophages in BALF and parenchymal haemorrhage assessed semiquantitatively by histopathological analysis. Patients with >or=20% haemosiderin-laden macrophages in BALF showed a significantly increased mortality rate (p = 0.047) compared to those with <20%. In patients with an acute onset of diffuse lung infiltrates and respiratory distress, >or=20% haemosiderin-laden macrophages in BALF can occur with DAD, and is not necessarily diagnostic of DAH. The finding of >or=20% haemosiderin-laden macrophages in BALF is associated with a worse prognosis in patients with DAD.