Smad proteins activated by TGF‐β form complexes with Smad4. Upon activation, these complexes translocate to the nucleus of the cell, where they induce transcription of genes related to inhibition of cell growth, cell differentiation and apoptosis. We investigated the role of Smads in the TGF‐β–mediated signal‐transduction cascade in 4 human cervical cancer cell lines: HeLa, Caski, HT‐3 and SiHa. Based on our results, SiHa cells show low mRNA expression of mutated Smad4 (Gly²³⁰Ala, Ala⁴⁸⁸Val) and of Smads 2, 3, 5 and 6. SiHa cells were likewise defective in TGF‐β signaling, as evidenced by a lack of significant growth inhibition following TGF‐β treatment. In addition, TGF‐β did not induce transcription of the PAI‐1 gene or change Smad protein levels. Introduction of Smad3 and/or Smad4 into SiHa cells restored TGF‐β signaling, as determined by activation of the 3TP‐lux reporter gene and by prominent apoptotic cell death with PAI‐1 induction. Analysis of the downstream targets activated by TGF‐β yielded rapid activation of p38 with subsequent phosphorylation of the transcription factor ATF‐2 but unchanged SAPK/JNK activation in the 4 cervical cancer cell lines. Our findings demonstrate that (i) decrease of Smad4 mRNA expression is closely associated with defective TGF‐β response and lack of growth inhibition, (ii) activation of PAI‐1 by TGF‐β may be Smad4‐dependent and (iii) the Smad and the p38 cascades are triggered by TGF‐β independently of each other in human cervical cancer. © 2001 Wiley‐Liss, Inc.