Piglets were exposed orogastrically to Escherichia coli to enable study of the duration of anti-adhesive and bactericidal activities of milk of sows vaccinated with a K88 enriched E coli vaccine. There was a marked increase in the number of the challenge strain in the digestive tract of weaned piglets of all ages (between 888 and 2144 per cent). In contrast, there was a decrease in their number (75 per cent) in the day-old colostrum-fed piglets. When the piglets were two weeks old milk was still capable of reducing the rate of proliferation of the pathogen but at five weeks it proliferated at equal rates in the digestive tract of both suckling and weaned litter-mates. The rate of adhesion of the K88 positive E coli to the small intestine of colostrum deprived piglets was high (5 x 108/g). Rate of adhesion fell gradually in weaned piglets from 5.4 x 107/g at two weeks to 2.0 x 106/g at four to five weeks of age. In contrast, resistance of the small intestine of suckling pigs to adhesion by K88-positive E coli remained relatively stable through the five week period of nursing bacterial counts ranging from 5 x 104/g to 3 x 104/g of tissue.