The transmission of anti-Salmonella agglutinins from actively immune mothers to their young was studied. Transmission of passive immunity in the hedgehog occurs both before and after birth, but the greater part occurs after birth. Concentration quotients (C.QS) ranging from 1/32 to 1/8 were obtained in five young sampled before suckling. C.QS of 1/2 were obtained in suckling young at 4 to 6 days of age, and in the young of two litters the C.QS were between 1/4 and 1/2 during the first 20 days of lactation. Subsequently the serum titres of the young declined. Uptake of antibody from the milk by the gut occurs during the first 20 days of lactation, and probably continues up to 30 days of age. In none of the young sampled did the serum titre equal that of the mother. The milk titre shortly after birth was 50% of the maternal serum titre and this proportion was maintained throughout the lactation period. Suckling hedgehogs given a single injection of Brucella abortus at from 9 to 21 days of age produced low circulating titres after 6 days, and are thus able to produce specific agglutinins during the period when antibody is being absorbed from the milk.