The mandatory reporting and investigation of bovine abortions provides a system for the surveillance of the progress of the Brucellosis Eradication Scheme and a warning of resurgence of brucellosis in tested herds. Before the scheme was introduced in 1971, about a quarter of all abortions were caused byBrucella abortus. By 1976, the percentage of abortions due toBrucellain herds under test for brucellosis had been reduced to 3.4%. MostBrucellaabortions occurred during the seventh and eighth months of gestation. Cows in the 4- to 6-year-old age group were at greater risk of aborting fromBrucellainfection than heifers. Approximately 94% of all aborting cows were in herds which experienced three or fewer abortions. Less than 4% of herds experienced four or more abortions annually. In most cases of abortion due to brucellosis, more than one diagnostic test yielded positive results. However, 13.3% of cases were recognised by positive bacteriological results alone.