A total of 446 sera from 245 patients with primary or secondary infertility, all of whom were examined laparoscopically, 117 patients with Chlamydia trachomatis-positive cervical swabs, and 84 control persons (50 obstetric patients and 34 female blood donors) were tested for antibodies to Chlamydia trachomatis and to Chlamydia pneumoniae with the microimmunofluorescence (MIF) test. MIF test antibody rates were highest in patients with complete tubal occlusion (73%) and in patients with proven Chlamydia trachomatis infection (74%), whereas only 9 to 10% of the control group showed Chlamydia trachomatis antibodies. Reaction to the 60 kDa antigen of Chlamydia trachomatis, a heat-shock protein (hsp) analogue, has been suggested as a possible marker for the development of chronic sequelae after Chlamydia trachomatis infection. Immunoblot analysis of 222 sera (169 infertility patients, 20 antigen-positive patients, and 33 mothers) showed a significantly higher anti-hsp antibody rate in patients with complete tubal occlusion than in infertility patients with normal fallopian tubes (76% vs. 19%, p < 0.001). The presence of antibodies not only to Chlamydia trachomatis but also to Chlamydia pneumoniae in the MIF test was associated with a significantly higher rate of anti-hsp antibodies and with complete tubal occlusion. This association did not appear to be due to cross-reactivity between Chlamydia pneumoniae and Chlamydia trachomatis antibodies in the MIF test.