Transforming growth factor-β (TGF-β) plays a complex role in skin carcinogenesis, acting as a suppressor early in tumor development but later as a promoter. Smad proteins are important intracellular mediators of TGF-β signaling. To determine the effect of disrupting Smad genes and TGF-β signaling on chemically induced skin carcinogenesis in mice, transgenic mice heterozygous for Smad2 or Smad3 deletions and wild-type controls were treated with topical dimethylbenzanthracene for 7 months. Tumor multiplicity, type, and degree of differentiation were assessed by histopathology and immunohistochemistry. Smad3^± mice developed significantly fewer tumors than the wild-type group (P < 0.05). This indicated a possible oncogenic function for Smad3 in skin carcinogenesis. Smad2^± mice formed less-differentiated tumors than their wild-type counterparts, supporting a tumor suppressor role for Smad2. There was a significant difference (P < 0.05) in tumor type between Smad2^± and Smad3^± groups, suggesting that Smad2 and Smad3 may regulate different targets.