Prior analyses from the National Institute of Mental Health Treatment of Depression Collaborative Research Program indicated that patients' expectancies of treatment effectiveness (S. M. Sotsky et al., 1991) and the quality of the therapeutic alliance (J. L. Krupnick et al., 1996) predicted clinical improvement. These data were reanalyzed to examine the hypothesis that the link between treatment expectancies and outcome would be mediated by patients' contribution to the alliance. Among 151 patients who completed treatment, this hypothesis was supported, suggesting that patients who expect treatment to be effective tend to engage more constructively in session, which helps bring about symptom reduction. Therapists' expectancies for patient improvement also predicted outcome, although this association was not mediated by the alliance. None of the expectancy scales interacted with alliance ratings in the prediction of clinical improvement.