The carcinogenic potential of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) was examined in Syrian golden hamsters, at different dose levels. Twenty-one percent of the hamsters that received a total of 600 micrograms/kg body weight of TCDD either by the s.c. or i.p. route developed squamous cell carcinomas of the skin of facial region within 12-13 months from the beginning of the experiment. Neoplasms were not observed in any other organs. These studies suggest that TCDD may be a complete carcinogen in hamsters, the species most resistant to the toxic effect of this compound.