Rikkunshi-to, a gastrointestinal function regulatory traditional Chinese herbal (Kampo) medicine, has recently been evaluated for its clinical usefulness in stress and depression. This medicine has modulatory effects on the hypothalamo-pituitary-adrenal axis and autonomic nervous function. We examined the effect of Rikkunshi-to and the other gastrointestinal function regulatory Kampo medicines, Hange-shashin-to, Hange-koboku-to, and Ninjin-to, on the plasma levels of adrenocorticotropic hormone (ACTH) and cortisol under stress conditions by repetitive blood sampling. Rikkunshi-to, Hange-shashin-to, and Hange-koboku-to significantly suppressed increases in plasma ACTH-immunoreactive substance (IS) levels compared with the response to a placebo. Rikkunshi-to and Hange-shashin-to significantly suppressed increases in plasma cortisol levels compared with the response to placebo. Ninjin-to had no significant effect on plasma ACTH-IS and cortisol levels. In this study, Rikkunshi-to, Hange-shashin-to, and Hange-koboku-to (partially) regulated plasma ACTH and cortisol levels under stress. These modulatory effects might be beneficial in stress-related disease and suggest that these medicines have clinical pharmacologic activity.