Unstimulated whole saliva was collected from 203 uninfected individuals at various ages from birth until adulthood. Levels of specific antibodies against Escherichia coli O antigens of secretory IgA, secretory IgM and IgG, as well as total amounts of SIgA, were determined using ELISA. Levels of SIgA antibodies found in adults were approached by the age of 12 months, but high levels could be attained earlier, presumably in response to antigenic exposure at the mucosal level. During the first few months of life, secretory IgM antibodies appeared in the saliva, possibly compensating for the relative lack of IgA.