of CA-4 showed potent antitubulin activity and cytotoxicity against murine Colon 26 adenocarcinoma in vitro. Some of the compounds which were potent in vitro were evaluated in the murine tumor model Colon 26 in vivo. Among these, 13bHCl, 21aHCl, and 21bHCl showed significant antitumoractivity in the animal model, while CA-4 was ineffective. 13bHCl and 21aHCl were further evaluated in two murine tumor