The phorbol ester 12-0-tetradecanoylphorbol-13-acetate (TPA), teleocidin, and two polyacetate tumor promoters (aplysiatoxin and debromoaplysiatoxin) have been tested for their effect on colony forming efficiency (CFE) of rat tracheal and nasal turbinate epithelial cells. In rat tracheal epithelial (RTE) cells, all four compounds stimulated colony formation by up to eight-fold using picomolar concentrations of aplysiatoxin and teleocidin, whereas TPA and debromoaplysiatoxin were effective in the nanomolar range. In addition, teleocidin and the other promoters increased the number of cells in colonies by 3-5 fold resulting in larger colonies, most notably above concentrations that maximally stimulated CFE, In contrast, rat nasal epithelial cells were only marginally stimulated by these tumor promoters to form colonies. The results indicate that there is regional specificity in responses to tumor promoters and RTE cells can act as very sensitive biological indicators of the presence of these three classes of tumor promoters with diverse structure. (Copyright (c) Carcinogenesis vol. 8 no. 1 p. 179-181, 1987.)