Decreased secretion rate of salivary markers of mucosal immunity, and in particular salivary immunoglobulin A (sIgA), have been implicated as risk factors for subsequent episodes of respiratory infection in athletes. IgA is the predominant Ig in mucosal secretions and acts with innate mucosal defences to provide the 'first line of defence' against pathogens and antigens presented at the mucosa. As well as summarising the evidence concerning the effects of acute exercise and longer-term intensive training on these markers of mucosal immunity, this review explores the factors that impact upon salivary responses to exercise, such as method of saliva collection, stimulation of saliva collection and the method of reporting s-IgA data. The influence of adequate hydration and nutritional supplementation during exercise as well as exercising in extreme environmental conditions on salivary responses is also explored. Finally, the possible mechanisms underlying the acute and longer-term of effects of exercise on salivary responses are examined, with particular emphasis on the potential role of the sympathetic nervous system and the expression and mobilisation of the polymeric Ig receptor. INTRODUCTIONOver the past two decades a growing body of evidence has supported the notion that both acute, strenuous exercise and intensive periods of physical training are associated with immune suppression and this may be linked to the apparent higher incidence of upper respiratory tract infections (URTI) in highly conditioned athletes (1,2). The acute decrease in immune function is transient and is dependent on the exercise intensity and duration. Repeated activity with insufficient recovery, such as during heavy periods of training and competition, appears to exacerbate the situation leading to a chronic depression of several aspects of immune function (3)(4)(5). Although the majority of studies have concentrated on continuous endurance-type activities such as distance running, cycling and swimming, evidence to support the concept of an exercise-induced immune depression has also been found following high-intensity intermittent activities such as football and tennis as well as high intensity resistance exercise (6-8).In contrast to the effects of intensive exercise on immune function, moderate amounts of physical activity in previously sedentary individuals, such as 30 min of brisk walking on most days of the week, are associated with either little effect on (9,10) or elevations (11,12) of markers of immunity and such activity has been associated with a lower incidence of URTI compared with sedentary individuals (1,9,11). The relationship between the amount of exercise and incidence of URTI has been proposed by Nieman (13) as a J-shaped curve and is largely supported by epidemiological data (9,11,14,15). However, identifying a definitive link between prevalence of URTI and any exercise-induced alterations in cellular and mucosal immunity has proved more difficult, not least because of the many confounders that could influence...