During an investigation of pig abortions and stillbirths in Northern Ireland, leptospires were isolated from 55 of the 78 litters examined. Strains belonging to four serogroups (Australis, Icterohaemorrhagiae, Hebdomadis and Autumnalis) were recovered but leptospires of the Australis serogroup accounted for 91 per cent of the isolates. Two serovars of the Australis group bratislava and muenchen, were identified.