Inducing depressed and anxious individuals to write about their personal goals decreases natural killer (NK) cell activity, revealing a psychobiological pathway whereby experiences of failure can influence health (Strauman et al., 1993). However, it is unclear whether similar effects also occur in non-distressed individuals. This study used the same writing task to examine the acute physiological effects of presenting idiographic success and failure feedback by priming self-congruencies or self-discrepancies on three occasions (including a control condition). Blood samples were collected after each writing session to determine NK activity, and the number and type of lymphocytes in circulation were enumerated to help explain the cytolytic changes. The two self-relevant priming conditions were associated with significant alterations in immunity, and the high self-discrepant participants were more responsive. Both self-congruent (success) and self-discrepant (failure) priming induced significant shifts in mood, which partially mediated immune alterations but did not account for them completely. If repeated and sustained over time, incidental activation of self-discrepancies and self-congruencies could account for individual variation in immune responses.