OBJECTIVE: To determine whether placebo responses can be explained by characteristics of the patient, the practitioner, or their interpersonal interaction. METHODS: We performed an analysis of videotape and psychometric data from a clinical trial of patients with irritable bowel syndrome who were treated with placebo acupuncture in either a warm empathic interaction (Augmented, n = 96), a neutral interaction (Limited, n = 97), or a waitlist control (Waitlist, n = 96). We examined the relationships between the placebo response and a) patient personality and demographics; b) treating practitioner; and c) the patient-practitioner interaction as captured on videotape and rated by the Psychotherapy Process Q-Set. RESULTS: Patient extraversion, agreeableness, openness to experience, and female gender were associated with placebo response, but these effects held only in the augmented group. Regression analyses controlling for all other independent variables suggest that only extraversion is an independent predictor of placebo response. There were significant differences between practitioners in outcomes; this effect was twice as large as the effect attributable to treatment group assignment. Videotape analysis indicated that the augmented group fostered a treatment relationship similar to a prototype of an ideal healthcare interaction. CONCLUSIONS: Personality and gender influenced the placebo response, but only in the warm, empathic, augmented group. This suggests that, to the degree a placebo effect is evoked by the patient-practitioner relationship, personality characteristics of the patient will be associated with the placebo response. In addition, practitioners differed markedly in effectiveness, despite standardized interactions. We propose that the quality of the patient-practitioner interaction accounts for the significant difference between the groups in placebo response.