In a naturalistic pre-post design, samples of saliva were collected from the members of a professional chorale during an early rehearsal (n=31), a late rehearsal (n=34) and a public performance (n=32) of Beethoven's Missa Solemnis. As measures of immune system response, mean levels of secretory immunoglobulin A increased significantly, as a proportion of whole protein, 150% during rehearsals and 240% during the performance. Cortisol concentrations decreased significantly an average of 30% during rehearsals and increased 37% during performance. As measured through performance perception rating scales, a group of emotions and other experiential states that singers associated with professional singing were highly predictive of changes in level of secretory immunoglobulin A during the performance condition, but the results for the rehearsal conditions were not significant. The best multiple regression model for performance level of immunoglobulin A (p < .0015) included seven emotional, cognitive, and evaluative variables generally associated with choral singing, including levels of mood before and during singing, stress, relaxation, feeling "high," detachment/engagement, and specific satisfaction with the immediate performance.