Pregnant sows were immunised with hen-egg albumin and intradermal tests were carried out on their piglets after birth. Colostrum-deprived piglets from immunised sows were hypersensitive to egg albumin, and it is postulated that these piglets may have been sensitised through the transference of small amounts of antibody across the placental barrier. Antibody present in colostrum also conferred passive sensitisation. The symptoms and lesions that developed in the piglets after intravenous challenge were characteristic of anaphylactic shock, and were compared with those found in naturally occurring E. coli infection.