The Smad6 and Smad7 genes are members of the Smad family, involved in the transforming growth factor-beta (TGF-beta) signaling pathway. Mutations in TGF-beta receptors and their cytoplasmic elements of transduction signals commonly accompany various cancers. Using PCR-SSCP analysis we searched for the presence of Smad6 and Smad7 gene mutations in 30 human ovarian cancers and 4 ovarian cancer cell lines, and found that 12 cases (35.3%) had a polymorphism in intron 2 of the Smad6 gene and that 8 cases (23.5%) had a polymorphism at codon 208 in the Smad7 gene. Because these polymorphisms were not accompanied by amino acid substitution, the present results show that the mutations in the Smad6 and Smad7 genes are unlikely to be involved in human ovarian cancers.