Statistical data were collected from 20 sheep flocks in which enzootic abortion of ewes (EAE) was diagnosed by examination of fetal material and maternal blood samples. The abortion rate in the 10,645 ewes in these flocks was 7.6 per cent. Thirteen of the flocks were fully vaccinated against EAE but the abortion rate in these was still in the order of 6.5 per cent. EAE was the major cause of the problem as ascertained from the laboratory examination of samples from a wide range of cases of abortion. There is therefore evidence that, in some flocks in south east Scotland, the efficacy of the vaccine against EAE is unsatisfactory. The reasons for this are discussed.