To determine the salivary secretory immunoglobulin A (sIgA) response to repeated bouts of unaccustomed, downhill running (eccentrically biased) and examine potential protective immunological adaption from a repeated bout effect. Eleven active but untrained males (age: 19.7±0.4 years; VO2peak: 47.8±3.6 ml kg-1 min -1) performed two 60 min bouts (Run 1 and Run 2) of downhill running (-13.5% gradient), separated by 14 days, at a speed eliciting 75% of their VO2peak on a level grade. Saliva samples were collected before (baseline), immediately post exercise (IPE), and every hour for 12 h and every 24 h for 6 days after each run. Salivary sIgA concentration was measured and sIgA secretion rate was calculated. Results were analysed using repeated measures ANOVA (12 h period: 2x14; 24 h intervals: 2x7; p = 0.05) with Tukey post-hoc tests where appropriate. Results are reported as means ± SE. There was a significant (p 0.0001) interaction effect for sIgA secretion rate, IPE, with higher values after Run 2, as well as a significant (p 0.01) time effect with elevated levels IPE and between 24 h and 144 h. There was a run effect (p 0.0001), with the sIgA secretion rate significantly higher after Run 2. Repeated bouts of unaccustomed, eccentrically biased exercise induced alterations in the salivary sIgA secretion rate. This may serve as a protective mucosal adaptation to exercise-induced tissue damage.