Young vertebrates have limited capacity to synthesize antibodies and are dependent on the protection of maternally transmitted antibodies for humoral disease resistance early in life. However, mothers may enhance fitness by priming their offspring's immune systems to elevate disease resistance. Transgenerational induced defences have been documented in plants and invertebrates, but maternal priming of offspring immunity in vertebrates has been essentially neglected. To test the ability of mothers to stimulate the immune systems of offspring, we manipulated maternal and offspring antigen exposure in a wild population of birds, pied flycatchers (Ficedula hypoleuca). We show that immunization of the mother before egg laying apparently stimulates a transgenerational defence against pathogens by elevating endogenous offspring antibody production. If the disease environments encountered by mothers and offspring are similar, this transgenerational immune priming may allow young to better cope with the local pathogen fauna.