Among new taxoids, taxuspines A - H and J - T (1 - 19), and known taxoids 20 - 56 containing taxol (56) and taxol-type compounds 37 -44 with an N-acylphenylisoserine group at C-13 and an oxetane ring at C-4 and C-5 isolated from stems and leaves of the Japanese yew Taxus cuspidata Sieb. et Zucc., nontaxol-type compounds 4 and 32 remarkably reduced CaC12-indaced depolemerization of microtubules. Furthermore, some non-taxol-type compounds 2, 3, 9, 24, 25, 27, and 28 increased cellular accumulation of vincristine in multidrug-resistant tumor cells as potent as verapamil, while taxol (36) and taxol-type compounds did not show such an activity. In addition, the non-taxol-type compounds enhancing vincristine accumulation inhibited competitively binding of azidopine to P-glycoprotein. These results suggest that some non-taxol-type taxoids may be useful for overcoming multidrug resistance in tumor cells.