Phagocytosis of Treponema pallidum by cytokine-activated macrophages aids bacterial clearance and lesion resolution in early syphilis. To investigate the cytokine profiles of cells infiltrating primary and secondary syphilis lesions, reverse transcription and polymerase chain reaction (RT-PCR) were used to detect cytokine mRNA in 13 lesion biopsies. Both primary and secondary lesions contained mRNA encoding interleukin (IL)-2, interferon-gamma (IFN-gamma), IL-12p40, and IL-10. In contrast to a lesion from a patient with recurrent herpes simplex virus type 2, no message for IL-4 could be detected in any of the syphilis lesions, and 10 of 13 had no mRNA for IL-5 or IL-13. These findings are consistent with a Th1-predominant local cellular response activating macrophages and support the hypothesis that IFN-gamma-activated macrophages are primary effectors in treponeme clearance.