This review focuses on saliva as a measure of mucosal immunity in man. The review will cover studies of parameters that modify the early ontogeny patterns of mucosal immunity and the impact of infections and physiological variables on the human mucosal immune system. The most significant modifiers of human mucosal immunity are events that occur in the neonatal maturation period and, later in life, the interplay between the immune system and the neuroendocrine systems. IgA antibodies are the predominant isotype involved in the human mucosal immune response and are important for protection at mucosal surfaces. The level of IgA in mucosal secretions is modified by antigenic stimulation as well as by many physiological variables. Studies have also revealed that IgM plays a significant immunoregulatory role at mucosal surfaces, particularly during episodes of infection or stress. The detection patterns of IgD in saliva of neonates suggests a role for IgD in the initial maturation process of mucosal immunity. The role of IgG at mucosal surfaces is unclear and although IgG may play a compensatory role in IgA deficiency, the detection of high levels of IgG in saliva appears to be associated with periods of increased membrane permeability.