DNCB is an antigen that stimulates the cell-mediated response in a sensitized host. The purpose of this study was to define the effect DNCB would have on a standard model system for oral carcinogenesis, theorizing that tumorgenesis would be delayed or inhibited. Fifty-six Syrian hamsters were divided into four groups. In group A (DNCB/DMBA), the right buccal pouch of twenty animals was treated with 2% DNCB in orabase, twice a week, and 0.5% DMBA, three times a week, for 10 weeks. In group B, twenty animals received DMBA only. In group C, six animals received DMBA in Orabase. In group D, ten animals received DNCB in Orabase only. The animals were killed at 6, 12, 16, and 20 weeks. The results indicate that there were no differences in the latent period or in the histologic characteristics of the epidermoid carcinomas that developed. However, there was sensitization of the buccal pouch in pouches painted with DNCB, in that gross and histologic evidence of a delayed sensitivity reaction was demonstrated.