Peripheral lymphocytes in uninfected fertile controls, women with various histories of Chlamydia trachomatis infection, pelvic inflammatory disease (PID) and infertility not due to C. trachomatis infection (endometriosis) were cultured overnight with PHA mitogen and the 60 kDa chlamydial heat shock protein. Plasma samples were then assayed for levels of gamma-interferon and IL-10 using a commercial ELISA system. Women with PID and those with a history of multiple C. trachomatis infections showed reduced gamma-interferon production in response to cHSP60, not seen in women infected only once and those with infertility due to other causes (endometriosis). Secretion of IL-10 in response to cHSP60 did not vary significantly across the various patient groups, though all patients showed elevated levels of total IL-10 compared with uninfected controls.