Chlamydia trachomatis infects the upper genital tract of millions of women, causing infertility and pelvic inflammatory disease, yet the inflammatory response to C. trachomatis infection is poorly understood. The cytokine response and the phenotype of infiltrating lymphocytes during C trachomatis infection of fimbria and ampulla autografts in subcutaneous pockets in Macaca nemestrina were characterized. About two-thirds of the infiltrating lymphocytes were CD8 T cells, with the remainder being CD4 T cells and B cells. Interleukin (IL)-2, IL-6, IL-10, interferon-gamma (IFN-gamma), and perforin mRNA were produced by the infiltrating cells, but IL-4 mRNA was absent. The presence of CD8 T cells and perforin mRNA suggest that activated cytolytic T cells are present. The presence of IL-2 and IFN-gamma mRNA and the absence of IL-4 mRNA suggest that Th1-type cytokines predominate during the acute phase of C. trachomatis infection of the upper genital tract.