Before weaning, some young pigs in a research piggery excreted in their faeces a weakly haemolytic non-enterotoxigenic serotype ofEscherichia coli. After weaning, all of the pigs excreted strongly haemolyticEscherichia coliof known enteropathogenic serotypes (0-138 and 0-139). The 0-138 serotype produced vero cell toxin, whilst the 0-139 serotype elaborated heat labile enterotoxin. Haemolytic enterotoxigenicE. coliwere also recovered from three-week-old unweaned piglets with so-called ‘milk scours’ and from pigs with post-weaning diarrhoea on two local commercial piggeries. Selected haemolytic isolates were compared using serotyping, bacterial restriction endonuclease DNA analysis (BRENDA) and incompatibility grouping. The three typing methods divided most of the isolates into the same groupings; the exceptions were two isolates with the same BRENDA pattern and incompatibility group, but with different H-serotypes, and eleven isolates with the same serotype and BRENDA pattern but which showed differences in colony compatibility such that they were divided into five subgroups of a single incompatibility type.