Adventitious roots were produced directly from root segments of Panax ginseng seedlings when cultured on an MS solid medium containing 3.0 mg $L^{-1}$ IBA. Omitting $NH_4NO_3$ from this medium greatly enhanced both the frequency of adventitious root formation and the number of roots per explants. This frequency declined markedly with the age of the root, but could be increased through repeated sub-culturing events. A two-step procedure that included $NH_4NO_3$ free media for the first two weeks of culture, followed by transfer onto media containing $NH_4NO_3$ for another four weeks, greatly improved total fresh weights of these adventitious roots compared with a method of continuous culture over six weeks in media that always contained $NH_4NO_3$. Expression of the genes involved in triterpene biosynthesis was analyzed by RT-PCR. Ginsenoside contents were enhanced by the omission of $NH_4NO_3$ and were also greatly increased by treatment with methyl jasmonate.