Immunotherapy in cancer patients is a very promising treatment and the development of new protocols and the study of the mechanisms of regression is imperative. The objective of this study was to evaluate the production of cytokines in helper T (CD4(+)) lymphocytes during immunotherapy with pegylated IFN-alpha in patients with cervical intraepithelial neoplasia (CIN). We conducted a prospective study with 17 patients with CIN II-III using immunotherapy with pegylated IFN-alpha subcutaneouly weekly, and using flow cytometry we evaluated the peripheric CD4(+) T lymphocytes. The results show that in the regression group the patients presented a significant increase in the amount of IFN-gamma during the entire immunotherapy, compared with the group without a response. The amount of CD4(+) T lymphocytes positive for IL-2, IL-4, IL-10 and TGF-beta is significantly lower in patients with good clinical response. The results also demonstrate that patients with regression have a higher amount of intracellular TNF-alpha in CD4(+) T lymphocytes before the start of treatment. Analyzing these data sets, it can be concluded that immunotherapy is a viable clinical treatment for patients with high-grade CIN and that the regression is dependent on the change in the immune response to a Th1 pattern.