Remark : Result: The inhibitory effects on P-gp mediated digoxin transport were investigated in MDR1-MDCKII cells. Emodin, 18 beta-GA, DAG, and 20 (S)-GF1 exhibited significant inhibition (> 50%) on P-gp. However, the isomers or analogs of the 4 herbal constituents (chrysophanol, 18alpha-GA, AG, and Rh1) and the remaining tested compounds relatively weak inhibition on digoxin transport in this cell model. The concentraion-dependent inhibition on P-gp-mediated digoxin transport was further investigated for emodin, 18beta-GA, DAG, and 20(S)-GF1. Emodin was the strongest herbal inhibitor of P-gp, followed by 18beta-GA, 20(S)-GF1 and DAG. Consistent with the data obtained from MDR1-MDCKII cells, emodin, 18 beta-GA, DAG, and 20(S)-GF1 significantly inhibited digoxin transport (>50%), while chrysophanol, 18alpha-GA, AG, and Rh1 showed no effects or relatively weak inhibition on P-gp.