The capacity for mothers to transmit induced resistance against a specific parasite to their young may be an essential maternal effect that determines the fitness of offspring. In a previous study, antibodies against the Lyme disease agent Borrelia burgdorferi sensu lato were detected in kittiwake (Rissa tridactyla) eggs in relation to the exposure of birds to the tick vector Ixodes uriae. However, as yet, there has been no demonstration of a direct relationship between antibody concentrations in parents and young in a natural population. Here, we show, using the kittiwake–Borrelia system, the existence of a positive relationship between antibody concentrations in maternal serum and that in eggs and chick serum. No such relationship was found between paternal serum and eggs or young. These results suggest the existence of an adaptive maternal effect, an effect that should have important implications for the ecology and evolution of host–parasite interactions.