Pan masala, a dry powdered mixture of areca nut, catechu, lime, unspecified spices and flavoring agents, has gained widespread popularity as a chewing substitute in India. In this study, the carcinogenic and tumor-promoting potential of an ethanolic pan masala extract (EPME) was determined using skin of S/RVCri-ba mice and forestomach and esophagus of ICRC mice as the target tissues. Carcinogenic activity of pan masala was tested by painting the mouse skin for 40 weeks with EPME or by gavage feeding for 6 months. Following initiation with 9,10-dimethylbenz(a)anthracene (DMBA), carcinogenesis of mouse skin was promoted with different doses of EPME, while gastric- and esophageal-tumor-promoting activity was determined by administering EPME by gavage to animals initiated with diethylnitrosamine (DEN). The ability of EPME to effect progression of skin papilloma to carcinoma and cutaneous alterations after a single or multiple EPME treatment were also evaluated. EPME at 25 mg per dose promoted skin-papilloma formation between 30 and 40 weeks of treatment and enhanced the rate of conversion of papilloma to carcinoma. Induction of mild epidermal hyperplasia, dermal edema, increase in epidermal mitotic activity and the rate of epidermal and dermal DNA synthesis by EPME correlated well with its skin-tumor-promoting potential. In ICRC mice, EPME was inactive as a complete carcinogen, but effectively promoted the development of forestomach and esophageal papilloma and carcinoma in a concentration-dependent manner. The tumor incidence at 25 mg EPME per dose was comparable with that obtained in the 12-O-tetradecanoylphorbol-13 acetate(TPA)-treated group. The findings indicate that habitual pan-masala use may exert carcinogenic and co-carcinogenic influence.