Salivary IgA is the primary antibody of mucosal immunity. It has been suggested that chronic stress may lower levels of IgA and lead to an increased susceptibility to respiratory illness. It is also suggested that acute stress increases IgA during active coping (that involves mental effort or controllability, such as time-based mathematics or memory tests) and decreases it during passive coping tasks (with no mental effort required or uncontrollable, such as the passive viewing of disgust images). However, tasks often classed as stressors have produced consistent IgA effects in areas of passive coping and chronic stress. These inconsistencies might be a consequence of methodological issues, such as sampling procedures, or may reflect individual differences, for example how a task is appraised. This thesis examined appraisal effects with focus on control over a stressful event and a potential relationship with salivary IgA. Three different study designs were used to examine stress, appraised control and salivary IgA. To alter appraisal during passive coping, disgust images were presented as either real pictures or as fake effects from fictional films to change the participant's perception of control during the image presentations. The role of appraised control during a chronic stress situation was explored in caregivers, and finally, appraised control and subjective stress were investigated in relation to IgA daily for a week in undergraduates, alongside perceived stress and hassles from the prior month. Viewing disgusting images increased perceived stress, irrespective of whether the images were presented as real or fake. Crucially, control was lower and salivary IgA increased only in the group that were told the images were real. Appraised control over a chronic stressor of caregiving did not affect IgA, but neither did perceived stress. Finally, in undergraduates, stress measured at the same time as sampling showed a lower level of IgA on days rated the highest compared to lowest on stress, and appraised control had a negative correlation with IgA when averages were used over the week, but only in a sub-group of participants. Perceived stress or hassles from the prior month did not relate to IgA. The main conclusions are that a participant's appraisal of passive coping tasks can be altered and that this may lead to a change in their IgA response. The overall results challenge the view that IgA is a stress marker, as the only consistent effect of stress on IgA was its consistency. Yet inconsistent IgA responses are likely to be a recurring issue in research due to the sensitivity of IgA to a number of different methodological practices that may cause a direct effect, or may alter appraisals.