The differences among certain physiological changes occurring in response to mirthful laughter, directed relaxation, and verbal speech were investigated. These changes included amount of muscle tension, as measured with surface electromyography, in the forehead and in the upper body as recorded from the forearms bilaterally, peripheral surface skin temperature, heart rate, and respiration rate. The study sought to determine whether the net effect of laughter, as measured on these five variables after a three-minute refractory period, is a more relaxed state than existed before the laughter. Determination of the similarity between the changes following laughter and the changes following directed relaxation was made in comparison with the changes following verbal speech. Factors of prior anxiety, pre- and post-self-esteem levels, humor level, and laughter intensity were examined. Historical and theoretical perspectives were reviewed, as well as the known information on physiological responses to laughter.