This study of 37 children aged 3.5–5 years attending a single Australian pre-school for one school year establishes longitudinal data on (1) the development of total salivary immunoglobulins IgA, IgG, and IgM, and IgA antibody specific against E. coli O antigen; (2) the influence of age on these parameters; (3) the impact of season and infection on immune parameters; (4) environmental factors which affect the pattern of immunoglobulin ontogeny and antibody production. The gene discussed is CD40LG; the disease is infection.