Squamous cell carcinoma of the uterine cervix is one of the most frequent cancers affecting women worldwide. Carcinomas arise from cervical intraepithelial lesions, in which infection with high-risk human papillomavirus types has led to deregulated growth control through the actions of the viral E6 and E7 oncoproteins. The molecular mechanisms underlying progression to invasive tumor growth are poorly understood. One important feature, however, is the escape from growth inhibition by transforming growth factor beta (TGF-beta). Loss of chromosomal arm 18q is among the most frequent cytogenetic alterations in cervical cancers and has been associated with poor prognosis. Since the TGF-beta response is mediated by Smad proteins and the tumor suppressor gene Smad4 resides at 18q21, we have analysed the Smad4 gene for cervical cancer-associated alterations in cell lines and primary carcinomas. Here, we report Smad4 deficiency in four out of 13 cervical cancer cell lines which is due to an intronic rearrangement or deletions of 3' exons. All cell lines, however, showed either absent or moderate responsiveness to TGF-beta irrespective of their Smad4 status. In 41 primary squamous cervical carcinomas analysed, 10 samples showed loss of Smad4 protein expression and 26 samples a reduced expression. Altogether, our results strongly suggest that Smad4 gene alterations are involved in cervical carcinogenesis.