Autologous bone marrow transplantation was performed in a 48-year-old man with relapsed high grade lymphoma. Two hours after the marrow infusion he developed pulmonary infiltrates and adult respiratory distress syndrome (ARDS). The aetiology of ARDS in this setting is uncertain but probably relates to pulmonary infection and endotoxaemia present at the time of marrow infusion. As the number of transplant procedures increases, particularly in patients with relapsed or resistant disease, this complication may become more common. In the infected patient in whom it is more likely to occur, prevention may be possible by giving anti-endotoxin antiserum prior to marrow infusion.