Infective endocarditis has a high mortality and morbidity rate despite all available treatment. Little attention has been paid to the possible role of polymorphonuclear leucocytes in damage to the heart valves. It was postulated that if the elastases set free from these leucocytes could be neutralised, this would prevent damage to the heart valves. Alpha 1-antitrypsin (alpha 1-AT) in liposomes was used to neutralise elastases. This process on its own and in various combinations with ampicillin were compared in animal models. Evaluation was performed by measuring vegetation size, by blood and vegetation cultures, and by light microscopy of the damaged tissue. A statistically significant difference (t-test; P less than 0.005, with Bonferroni's correction for multiple comparisons) was found in vegetation size in the groups receiving ampicillin in liposomes, but the hypothesis that alpha 1-AT might reduce valvular damage was not proven.