This study addressed the notion that the progression of cervical cancer is associated with a T-helper 2 (TH2) immunodeviation by analysing cytokine expression in 60 cervical biopsy specimens, spanning the spectrum from normal cervical tissue to high-grade squamous intraepithelial lesions (SILs). The biopsies were analysed by immunohistochemistry for the expression of TH1 [interleukin-2 (IL2), interferon gamma (IFN gamma)] and of TH2-type cytokines (IL4, IL6). Positive cells were usually observed in the subepithelial connective tissue, where most CD4+ cells were also detected. The density of IL2+ cells was significantly lower in high-grade SILs than in normal tissues taken either from the ectocervix or from the transformation zone. In contrast, significantly higher densities of IL4+ cells and, to a lesser degree, IL6+ cells were found in SIL biopsies compared with histologically normal tissues taken from the adjacent ectocervical region. A significantly higher IL4+/CD4+ cell ratio was also found in high-grade SILs (82 per cent) than in normal cervical biopsies taken from the transformation zone of healthy women showing squamous metaplasia (27 per cent). The elevated density of TH2+ cells in SIL biopsies was associated with both the expression of HLA-DR by keratinocytes and a diminished number of intraepithelial Langerhans' cells (CD1a+). In conclusion, the increased TH2+/CD4+ cell ratio in SIL biopsies suggest the presence, during cervical carcinogenesis, of a TH2 immunodeviation that could participate in the immunoescape of preneoplastic cervical keratinocytes.