Vincristine [an antitumor agent] was administered to 60 rats in 4 groups in doses of 0.1, 0.3, 0.5 and 0.7 mg/kg. Histomorphologic investigation of the dentin and odontoblasts in the maxillary incisors after 1, 2 and 3 wk revealed a moderate to severe disturbance of dentin production in some parts of the incisors. In some of the affected areas the effect seemed to be reversible in that normal-appearing dentin was found pulpal to the dentinal derangements after 2 and 3 wk. The distribution and severity of the lesions were similar to those previously observed 3 days after injection of the same doses of vincristine.