Golden Syrian hamsters are evaluated as an animal model for phototherapy of early squamous cell carcinomas of the mucosa of the upper aerodigestive tract, the esophagus and the tracheobronchial tree. Carcinomas of this type are induced on the hamster cheek pouch mucosa by the application of the carcinogen 7,12 DMBA. For phototherapeutic expts. on the animals the authors utilized meso-(tetrahydoxyphenyl)chlorin (mTHPC). The same drug is currently in phase I, II clin. trials for ENT patients with superficial squamous cell carcinomas. By light induced fluorescence (LIF) the authors measured in vivo the kinetics of the uptake and removal of mTHPC in the normal and tumoral cheek mucosa and in the skin. The photodynamic therapy (PDT) reaction of the tissue after excitation of the photosensitizer by laser light at 652 nm was studied. Both pharmacokinetics and PDT efficacy are compared between animal model and clin. results with special emphasis on selectivity between normal and tumoral mucosa. These first expts. show that this tumor model in the hamster cheek pouch seems to be suitable for tests of a no. of PDT variables of new photosensitizers preceding their clin. application as well as for optimization of the multiple parameters of clin. phototherapy.