Vincristine, an alkaloidal substance derived from the plantVinca rosea(periwinkle), was discovered to have antitumor activity in animals in 1963 (1). Since then, the drug has been shown to be effective in a variety of human malignancies (2). Particularly striking has been its ability to induce complete hematologic remission of acute lymphoblastic leukemia. The increased use of vincristine has been associated with increased reports of accidental.The work reported herein was performed under the United States Navy Clinical Investigation Program, study number 81–16-1493. The animals involved in this study were procured, maintained, and used in accordance with the “Animal Welfare Act of 1966, as amended” and the “Guide for the Care and Use of Laboratory Animals” prepared by the Institute of Laboratory Animal Resources, National Academy of Sciences—National Research CouncilThe option or assertions expressed in this paper are those of the authors; and are not to be construed as official or as necessarily refecting the views of the Department of the Navy or the naval service at large.