A new antileukemic taxane alkaloid, cephalomannine (la), has been isolated from leaves, stems, and roots of Taxus wallichiana Zucc. Cephalomannine is closely related to taxol (lb), a previously characterized antileukemic alkaloid, which also occurs in T. wallichiana but in lesser amounts them cephalomannine. The new alkaloid and its hydrolysis products were characterized by nucleetr magnetic resonance, mass spectroscopy, and X-ray crystallography; taxol and two cytotoxic taxeme congeners were also identified. © 1981, American Chemical Society. All rights reserved.