Several experiences induced us to consider genital HPV infection as an expression of a local immunodeficiency. The aim of our study was to research the effect of immunotherapy on the lymphocyte subpopulations and Langerhans cells in vulvar condyloma. Twenty women with persistent vulvar condylomata, treated with 2,000,000 IU/die of beta-interferon for 15 days, were submitted to vulvar biopsy before and 2-5 months after medical treatment. The frozen sections obtained were assayed with the following monoclonal antibodies: OKT 4 (T helper lymphocytes), OKT 8 (T suppressor lymphocytes), OKB 7 (B lymphocytes) and S-100 protein (Langerhans cells). Using a morphometric evaluation, the average number of both intraepithelial and stromal lymphocyte subsets and of the intraepithelial Langerhans cells was assessed. In all the biopsies preceeding the medical treatment we found a low number of T helper lymphocytes both in the epithelium and stroma, with inversion of T4/T8 lymphocyte ratio and rare presence of Langerhans cells. In patients with a good therapeutic response (50-100% of condyloma reduction) we observed an increase in intraepithelial T4 lymphocytes and a decrease in both intraepithelial and stromal T8 lymphocytes. In cases with persistent disease after therapy, the histological pattern was similar to that observed in the first biopsy, with the exception of a significant increase in the average number of Langerhans cells. Our data correlate the clinical response to the immunotherapy with the histology of lymphocyte subsets in the vulvar condylomata. The increase in Langerhans cells observed in patients with negative response may be interpreted with a probable inability of these cells to promote the immune reaction.