Abstract Tissue enzymes, LDH, AST, ALT, AP, TACP and CK, were measured in amniotic fluid collected from ten chronically-catheterized (intra-amniotic) ewes from 90 to 105 days of gestation until abortion occurred or, in five ewes, the lambs were removed by hysterotomy. Bacterial contamination occurred either during or after surgery in six of the ewes; in eight ewes a test inoculum of Staphylococcus aureus was infused into the amniotic sac. All six enzymes increased in activity in the amniotic fluid just before foetal death or abortion. However, with the exception of one ewe in which amniotic fluid enzyme activity reached very high values, there were no parallel changes in the maternal plasma.