Secretory IgA in saliva (s-IgA) is a potential mucosal immune correlate of upper respiratory tract infection (URTI) status. Nutritional supplements may improve mucosal immunity, and could be beneficial to athletes who are at increased risk of URTI. In this study, 35 distance runners (15 female, 20 male, age 35 to 58 y) consumed a supplement of either bovine colostrum or placebo for 12 wk. Saliva samples were taken prior to training at baseline, monthly during supplementation, and 2 wk post supplementation. Median levels of s-IgA increased by 79% in the colostrum group after 12 wk intervention, and the time-dependent change from baseline value was significant (P = 0.0291). This significance was still apparent after adjusting for training volume and self-reporting of upper respiratory symptoms. This study has demonstrated increased s-IgA levels among a cohort of athletes following colostrum supplementation. While this result is statistically significant, its physiological interpretation must be viewed with caution due to the small numbers in this study and the large variability in s-IgA levels.