Haematological, biochemical and pathological changes were investigated in 214 sheep naturally infected with Fasciola gigantica in an endemic area in the Sudan together with 82 uninfected controls. Infected animals showed a clear decrease in erythrocyte counts, haemoglobin concentration and packed cell volume, a normochromic, normocytic anaemia, leucocytosis and eosinophilia. Serum concentrations of the enzymes glutamate dehydrogenase, sorbitol dehydrogenase and glutamate oxaloacetic acid transaminase were also elevated in the infected group, indicating hepatic damage. This was confirmed by histopathological changes, which comprised degenerative and necrotic changes in hepatocytes associated with haemorrhage, fibrosis, increased lobulation of the liver, mononuclear cell infiltration with haemosiderin deposition in fluke tracks and portal areas and the formation of granulomata around fluke eggs and fluke remnants. In the infected group there was slight hyperglobulinaemia and a marked hypoalbuminaemia, with a decrease in A/G ratio. A slight rise in the level of serum bilirubin was also observed.