Changes in psychological and physiological functioning following participation in Tai Chi were assessed for 33 beginners and 33 practitioners. The variables in the three-way factorial design were experience (beginners vs practitioners), time (morning vs afternoon vs evening), and phase (before Tai Chi vs during Tai Chi vs after Tai Chi). Phase was a repeated measures variable. Relative to measures taken beforehand, practice of Tai Chi raised heart rate, increased noradrenaline excretion in urine, and decreased salivary cortisol concentration. Relative to baseline levels, subjects reported less tension, depression, anger, fatigue, confusion and state-anxiety, they felt more vigorous, and in general they had less total mood disturbance. The data suggest that Tai Chi results in gains that are comparable to those found with moderate exercise. There is need for research concerned with whether participation in Tai Chi has effects over and above those associated with physical exercise.