A series of 12 semisynthetic discodermolide analogues, 2-13, have been prepared using natural (+)-discodermolide (1) and evaluated for in vitro cytotoxicity against cultured murine P-388 leukemia and A-549 human adenocarcinoma cells. These semisynthetic analogues showed a significant variation of cytotoxicity and confirmed the importance of the C-7 through C-19 molecular fragment for potency. Specifically, these analogues suggested the importance of the C-11 and C-17 hydroxyl groups and the C-13 double bond for the potency of discodermolide. The preparation, structure elucidation, and biological activity of these new analogues are described.