The effects of a large dose of vinblastine sulfate (2 mg/kg body weight) on proliferating odontoblast precursors and secretory odontoblasts in the continuously growing rat incisor were studied. The rats were killed 6 h, 24 h, 3 d and 7 d after vinblastine injection. Most cells in the proliferating zone contained arrested mitoses, or had perished after 24 h. After 3 and 7 d, the odontoblasts derived from this zone were reduced in number, and showed altered cell shapes. The odontoblasts had produced irregular dentin. The secretory odontoblasts had displaced nuclei and altered cell shapes after 24 h. Those most affected were opposite early mineralized dentin. In some incisors the cells had perished. In the protracted experiments almost all the odontoblasts were changed and had produced abnormal dentin. In the early mineralized dentin area, accumulations of cells were present after 3 d, and osteodentin-like material after 7 d.