To test and optimize photodynamic therapy of early cancers in the upper aero-digestive tract and esophagus, we sought an appropriate animal model, which was found in the 7,12-dimethylbenz[a]anthracene-induced early squamous cell carcinoma in the Golden Syrian hamster. This chem. induced neoplasm is shown, by histol. and immunohistochem., to pass through similar stages of early cancer development as its human counterpart. Its time sequence is highly reproducible, leading to a well differentiated carcinoma in situ and microinvasive carcinoma in the hamster cheek pouch over a period of 10 wk.