In this study, we evaluated the effects of Panax notoginseng root extract (NGRE) and its major constituents on SW480 human colorectal cancer cells. We used high performance liquid chromatography to determine the contents of major saponins in NGRE. The anti-proliferative effects were evaluated by the cell counting method, and concentration-related anti-proliferative effects were observed. At 1.0 mg/ml, NGRE inhibited cell growth by 85.8% (P<0.01), probably linked to the higher concentration of ginsenosides Rb1 and Rg1. The pharmacologic activities of notoginsenoside R1 and ginsenosides Rg1 and Rb1 on the cells were antiproliferative. We tested the effects of NGRE on DNA synthesis by measuring [3H]-thymidine incorporation. NGRE induced cell apoptosis at 0.5 and 1 mg/ml. Two-day treatment with 300 microM of notoginsenoside R1, ginsenosides Rg1 and Rb1 increased cell apoptosis significantly. Cell cycle and cyclin A assay showed that NGRE arrested cells in the synthesis phase and increased the expression of cyclin A remarkably. NGRE also enhanced the actions of two chemotherapeutic agents, 5-fluorouracil and irinotecan. Cell growth decreased more with the combined treatment of NGRE and 5-fluorouracil (or irinotecan) than with the chemotherapy agent applied alone, suggesting that notoginseng can reduce the dose of 5-fluorouracil (or irinotecan) needed to achieve desired effects. Further in vivo and human trials are warranted to test whether notoginseng is a valuable chemo-adjuvant with clinical validity.