In this study, we examined the secretory immune system, the body's first line of defense against invading organisms, and its relation to daily fluctuations of mood. Specifically, secretory immunoglobulin A (sIgA) was studied. Unlike other psychoimmunity studies that examined all sIgA protein regardless of specificity to invading organisms, ours examined an antigen-specific sIgA response to the oral administration of a harmless protein (rabbit albumin) and monitored the antibody produced in response to the protein. Dental students recorded their daily mood thrice weekly for 8 1/3 weeks, and parotid saliva was obtained from subjects during these contacts. Using a within-subjects analyses strategy, we found that antibody response was lower on days with high negative mood relative to days with lower negative mood, and conversely, sIgA antibody response was higher on days with high positive mood relative to days with lower positive mood. Results from total sIgA protein were in the opposite direction, although not significantly so. These results extend our knowledge of immunological changes and mood, and they suggest that minor life events' role in health may be mediated by the secretory immune system.