The role of nutrition in the pathogenesis of E. coli enterotoxaemia was studied in weaned pigs inoculated with a field strain of E. coli O139:K82(B):H 4. Feeds extremely low in nutrients (5% crude protein, 4.6 MJ/kg digestible energy, 17% crude fibre) completely prevented the disease by inhibiting proliferation of the pathogenic bacteria in the intestine. This protective effect of the diet could not be used for disease control, because the pigs did not develop immunity. A diet moderately low in nutrients (8% crude protein, 9 MJ/kg digestible energy, 11% crude fibre) allowed proliferation of the inoculated bacteria to the point, where most of the pigs developed solid immunity and losses were significantly reduced. This diet combined with inoculation of the pigs with herd specific organisms allowed control of the disease in the field.