Surgical blades were contaminated by doing incisional biopsies on DMBA-induced cheek pouch carcinomas in hamsters. Contaminated blades were then used to: (1) make cytologic smears; (2) make incisions in the mucosal surface of the lower lip; (3) make incisions in the ventral surface of the tongue; (4) make incisions in the untreated left cheek pouch; and (5) make incisions in the pre-shaved back. One group of animals was killed three hr post-surgery. The second group was killed seven wk post-surgery. Tissues were excised and processed for microscopic study. Malignant cells were found in many of the incision sites of animals from the first group. In the animals of the second group, several tumors growing from the transplanted tumor cells were observed in the incision sites of the lower lips and the tongue. None was observed in the incision sites of the left cheek pouch or the back. Cervical lymph node metastases were found in approximately 50% of the animals of the second group.