Personality traits have emerged as the strongest identified predictors of response to antidepressant treatment of major depressive disorder (Peselow et al., 1992; Joyce et al., 1994). 18 subjects in the midst of a major depressive episode were treated with nefazodone in an open trial. All subjects completed Cloninger's tridimensional personality questionnaire (TPQ) before beginning treatment. A multiple regression analysis was performed in an attempt to replicate Joyce et al.'s (1994) finding that temperament type, as assessed by the TPQ, is a strong predictor of antidepressant response. A model involving TPQ reward dependence and harm avoidance scores, and their interaction, was found to significantly predict the response to nefazodone (r2 = 0.47, P < 0.027). When response was defined as a 50% decrease in HAM-D score at last visit, high reward dependence score alone significantly separated responders from nonresponders (Fisher's exact P = 0.050, df = 1). These results raise the intriguing possibility that TPQ scores may have direct clinical applications.