Tissue glutathione (GSH) and glutathione disulfide (GSSG) contents were quantitated in the skins of female SENCAR mice following the topical application of 12-O-tetradecanoylphorbol-13-acetate (TPA), and in the skin tumors generated by an initiation-promotion protocol. Total epidermal GSHt (GSH + GSSG) and GSSG contents were not reproducibly and significantly altered 0.5, 4 or 24 h after one or four topical applications of 1 microgram TPA, relative to the values obtained in age-matched, solvent-treated mice. Similar findings held for dermal GSHt at all times of analyses, and for dermal GSSG contents 0.5 and 4 h after TPA application. However, dermal GSSG contents were slightly elevated 24 h after TPA application. The GSHt and GSSG contents of skins initiated with 10 nmol 7,12-dimethylbenz[a]anthracene (DMBA) and harvested 17, 29 and 37 days after the cessation of chronic treatment with acetone (14 weeks, twice a week) were comparable to the values measured in age-matched, non-treated skins. In contrast, GSHt contents of papillomas harvested 17, 29 and 37 days after the cessation of chronic treatment with 1 microgram TPA (14 weeks, twice a week) were 2- to 4-fold greater than the values measured in non-treated mice, and DMBA-initiated, acetone-promoted mice, and the non-tumorous tissue adjacent to the papillomas. Comparable changes did not occur in papilloma GSSG contents. GSHt contents in squamous cell carcinomas (SCC) were twice the values measured in papillomas and 5- to 8-fold greater than the values measured in non-treated skins, and the non-tumorous tissue adjacent to SCC. Similarly, GSSG contents in SCC were elevated multifold relative to papillomas, non-treated skin and the non-tumorous tissue adjacent to SCC. Epidermal cell suspensions prepared by the trypsin-flotation procedure retained less than 2% of their original GSHt content and had reduced GSHt/GSSG ratios. Collectively these studies suggest that (i) if promoting doses of TPA induce oxidative stress in murine epidermis, it cannot be detected by measurements of GSH/GSSG; (ii) the antioxidant capacity of epidermal cells prepared by the trypsin-flotation procedure is severely compromised; and (iii) GSHt contents progressively increase during skin tumor ontogeny.