Severe lung injury (ARDS) has occasionally been observed after sclerotherapy for bleeding oesophageal varices. In order to study the effects of sclerosing agents, which may escape into the systemic circulation during treatment, seven sheep were given either ethanolamine oleate (n = 4) or sodium tetradecyl sulfate (n = 3) intravenously. A control group (n = 3) was treated identically with the others except it did not receive any sclerosing agent. The study showed that both sclerosing agents caused an immediate and severe fall in total respiratory compliance and arterial oxygen tension. There was a marked trapping of platelets in the lungs, which was also reflected by a drop in platelet count in peripheral blood. The lungs from the animals receiving sclerosing agents appeared moderately to severely congested and the wet/dry weight ratio of the lungs was significantly increased compared with untreated normal lungs (p less than 0.01). Histopathological examination revealed severe damage to the alveolar membranes, intraalveolar fibrino-haemorrhagic exudate, collapse of alveolar spaces and numerous eosinophilic leukocytes in the broadened, oedematous alveolar walls. It was concluded that the sclerosing agents used in this study, ethanolamine oleate and sodium tetradecyl sulphate, cause severe lung injury if given intravenously in sheep in doses corresponding to 25-50% of what is normally used during sclerotherapy in patients. The mechanism of this action may be that of an increased microvascular permeability causing marked alveolar damage and destruction of the blood gas barrier of the lungs.