A syndrome of acute dyspnoea after hunting in 16 Swedish hunting dogs is characterised. Radiographic pulmonary infiltrates interpreted as pulmonary oedema were found in the acute stage. In 12 dogs, the infiltrates regressed after five to 14 days. Subendocardial necrosis and pulmonary oedema were found at postmortem examination in four other dogs with acute and recurrent dyspnoea after hunting, and myocardial fibrosis in a further three dogs with a history of recurrent dyspnoea after hunting; none of these pathological changes was seen in dogs which had no previous history of dyspnoea after hunting. A pathogenetic mechanism is proposed whereby high catecholamine levels, present during hunting due to the stress of excitement and exercise, cause acute cardiac and pulmonary lesions in some susceptible dogs, similar to neurogenic or postictal pulmonary oedema.