Salivary IgA (SlgA) levels were determined in 1,539 normal children, aged between 8 months and 6 years. In four children (0.26%), an absence and in 25 children (1.62%) a relative defect, (less than 1 mg/dl) were found. These values are similar to those encountered in an adult male population. Conversely, the mean SlgA in all age groups we examined was much lower in comparison to the adult mean. This difference is particularly great for SlgA and much smaller for total salivary proteins. There was no difference between males and females, and no relation with personal or familial history of allergic and/or infectious episodes. The conclusions of this study are as follows: Absolute and relative SlgA defects, when found, are present from birth, The complete maturation of SlgA occurs after 6 years of age, The role of SlgA in the protection against allergic or infectious episodes perhaps ought to be revised.