Over a period of 15 months data were collected from abattoirs in Great Britain on 213,082 cattle and 362,838 sheep livers to determine the distribution and prevalence of damage by Fasciola hepatica. The stock came from 8239 farms, and from livestock markets in 81 counties. 53 per cent of the farms had sent affected stock, with significant percentages in eastern as well as the western counties of England and Scotland. 21 per cent of all cattle and 7 per cent of all sheep livers examined were affected. In both species, the percentage of adult stock affected was more than double that of young stock. The condemnation rate in cattle was relatively constant throughout the year. The effects of infestation are more widely distributed than has been generally recognised. Greater emphasis should be placed on the control of chronic fascioliasis in cattle.