A placebo effect on post-operative swelling was investigated as a possible model for studying psychological influences on recovery from surgery. 79 patients undergoing removal of impacted third-molars received one of five different procedures shortly after emerging from general anaesthetic. These included dentist-administered or placebo ultrasound (the latter given in two different ways to control for massage effects), untreated controls and a group instructed to apply facial massage to themselves. Pre- and post-operative measurements incSaveluded trait and state-anxiety, coping style, emotional state, pain, plasma cortisol and facial swelling. Cortisol levels correlated with anxiety and avoidant coping. Post-operative anxiety was negatively correlated with pre-operative arousal. Neither coping nor emotional state was affected by the treatments, but swelling was reduced by a placebo effect of ultrasound. Cortisol levels also responded, apparently to an effect of massage. The coping and emotional factors which we measured here cannot, therefore, explain the effects of this psychological procedure on post-operative recovery.