Positive emotional activities have been suggested as modifiers of neuroendocrine hormones involved in the classical stress response. To detect changes in these components during a mirthful laughter experience, the authors studied 10 healthy male subjects. Five experimental subjects viewed a 60 minute humor video and five control subjects did not. Serial blood samples were measured for corticotropin (ACTH), cortisol, beta-endorphin, 3,4-dihydrophenylacetic acid (dopac)--the major serum neuronal catabolite of dopamine, epinephrine, norepinephrine, growth hormone, and prolactin. Repeated measures analysis of variance showed that cortisol and dopac in the experimental group decreased more rapidly from baseline than the control group (p = 0.011, p = 0.025, respectively). Epinephrine levels in the experimental group were significantly lower than the control at all time points (p = 0.017). Growth hormone levels in the experimental group significantly increased during baseline (p = 0.027) and then decreased with laughter intervention (p less than 0.0005), whereas, the controls did not change over time (p = 0.787). ACTH, beta-endorphin, prolactin, and norepinephrine levels did not significantly increase. The mirthful laughter experience appears to reduce serum levels of cortisol, dopac, epinephrine, and growth hormone. These biochemical changes have implications for the reversal of the neuroendocrine and classical stress hormone response.