Background: Immunoglobulin-A in saliva (SIgA) has been proven to be decreased during periods of stress, a change that also correlates with increased disease risk. Hypothesis: Concentration of SIgA is negatively associated with dietary deprivation, negative moods, and anxiety. Methods: SIgA was evaluated as a marker of the severity of stress during a 19-day Royal Australian Air Force (RAAF) survival course, during which students experienced hunger, thirst, boredom, loneliness, and extreme heat and cold combined with demanding physical effort. There were 27 men and 2 women who participated. Students kept daily food diaries, from which daily intakes of energy and macronutrients were calculated. Saliva samples were collected on 9 d for the measurement of the ratio of SIgA to albumin (AIb). Students completed a health checklist and the State Anxiety Inventory on the same 9 d and the Profile of Mood States on 3 of the days. Results: Dietary restriction, consumption of alcohol, body mass loss, occurrence of upper respiratory tract infection, and negative emotions were negatively associated with SIgA:AIb. Conclusion: SIgA:AIb is a useful marker of the severity of stresses encountered during stressful training.