Secretory immunoglobulin A in saliva (sigA), self-reported stress, and arousal were measured in 16 undergraduates over a 4 hr time span during a class devoted to individual short oral presentations of academic work which was formally assessed. At the start of the class session, stress and arousal reports were already high, peaked at the time of an individual's presentation, and then declined to their lowest point half an hour after the presentation (the final measurement occasion). sigA rose to a peak immediately after the presentation and then declined. sigA effects were independent of changes in saliva flow, which did not significantly vary across occasions. These results add further evidence to support the view that immunological responses to psychological challenge can be very acute. Specifically, the results support earlier speculation that in the case of sigA the acute effects of a stressor may be transitory elevation of levels. The results are discussed in terms of possible rapid neuroendocrine modulation of the secretory process.