The growth responses of a variety of human intestinal bacteria to extracts of Panax ginseng and five other oriental medicinal Araliaceae were elraluattd in vitro and in vivo. The extracts enhanced the growth of Brifidobnnerilrm breve and B. longlim in media with or without carbon sources, suggesting that bifidus factors) might be involved in the phenomenon. This effect was most pronounced with water extract of P. ginseng, the growth of 27 bifidobacteria strains belonging to B adolescentis, B. longum, B. brim and B. infantis being greatly stimurated, whereas seven B. bifidum strains and other bacteria such as clostridia and Escherichin soli had little or no ability to utilise it for growth. Methanol extracts of p. ginseng were found to selectively inhibit growth of various clostridia including bifidobacteria. Paraputrificum, but this effect was not observed on other bacteria including bifidobacteria. The effect of ginseng extract intake (600 mg/day for two weeks) on the faecal microflora, pH, volatile fatty acids, ammonia, putrefactive products, and -glucuronidase, -glucosidase and nitroreductase activities, and on the blood components (triglyceride, total cholesterol and ammonia) were investigated using seven healthy human volunteers. The total concentration of faecal microflora including Bifidnkaderiifm app. during the period of ginseng extract intake %twas significantly unaffected from the preceding and subsequent control peroids. However, the frequency of occurrence of subjects having C. perfringens was significantly decreased. The faecal pH value was also significantly decreased, suggesting that the intake might increase the activity of Bifidobncterium spry. Other biochemical properties in faeces did not changed significantly. The levels of ammonia and triglycerid in blood were decreased with ginseng extract intake. These results may be an indication of at least one of the Pharmacological actions of p. ginseng as an adaptogen.