Samples of brain and lymphoid tissues from 1107 meat and bone meal-fed, culled adult pigs from 24 Irish farms were examined for evidence of transmissible spongiform encephalopathy (tse) by histopathological, immunohistochemical and Western blotting techniques. No evidence of deposits of abnormal prion protein suggesting the presence of tse was found. Neuropil vacuolation was apparent in the rostral colliculus in 64 per cent of the brains examined and neuronal vacuolation was present in the dorsal vagal nucleus in 15·4 per cent of the brains. However, similar lesions have been described in pigs used as controls in a bovine spongiform encephalopathy challenge experiment. Age-related changes were also observed, including spheroids in the funicular nucleus of 24·5 per cent of the pigs, deposits of lipofuscin in the trigeminal neurons of 13·75 per cent, and mineral deposits in the walls of vessels in the dorsal vagal nucleus of 0·6 per cent. Low-grade non-suppurative inflammatory changes of uncertain origin were observed in 4 per cent of the animals.