The incidence of Helicobacter pylori infection in very young children was determined, based on the emergence of specific IgG antibodies in sequential serum samples from birth to 2 years of age. The risk of acquiring H pylori infection in infancy as a result of maternal exposure to the organism was also assessed, based on the determination of maternal cord-blood antibodies. Serum IgG class H pylori antibodies were analysed in the cord blood samples of 195 newborns and in their follow up samples until the age of 2 years. Maternal antibodies were detected in the cord-blood samples of 21 children (10.6%). These antibodies disappeared in all but one child before 7 months of age and no new seroconversions occurred in these children. Ten originally cord-blood negative children seroconverted up to the age of 2 years (5.1%). It is concluded that a major proportion of H pylori infections observed in young adults in Finland are acquired during the first two years of life. Maternal seropositivity is not a straightforward risk factor for acquiring H pylori infection in infancy.