Ginsenosides, the bioactive components of ginseng, can be divided into two major groups, namely 20(S)-protopanaxatriol (e.g. Re, Rg1, Rg2, and Rb3) and 20(S)-protopanaxadiol (e.g. Rb1, Rb2, Rc, and Rd). Biological and environmental factors may affect the content of ginsenosides in different parts of ginseng plant. Evidence from pharmacokinetic and metabolic studies of Re demonstrated that (1) the absorption of Re is fast in gastrointestinal tract; (2) Re may be metabolized mainly to Rh1 and F1 by intestinal microflora before absorption into blood; and (3) Re is quickly cleared from the body.