The presence or absence of Chlamydia trachomatis antigen in the uterine cervix, uterine cavity and urinary tract was investigated by EIA (Chlamydiazyme) in 159 patients, in addition to the measurement of serum antibody titers in 120 of them by indirect enzyme immunoassay (IPAzyme). The results obtained were as follows. 1. The antigen was detected from one of the 3 sites in 13.8%. Patients in their twenties or younger had the highest positive rate (22.2%) and also the highest incidence of multiple lesions. 2. Patients with irregular hemorrhage from the uterine cavity had a high detection rate. 3. Detection rates for the uterine cervix, uterine cavity and urinary tract were 11.9%, 6.9% and 9.4% respectively. 4. As for overlap infection, the antigen was detected from 1, 2 and 3 sites in 7, 7 and 8 of 22 patients, respectively. 5. The incidence of active infection was significantly higher in antigen-positive patients than in antigen-negative patients, while no difference was observed in antibody titers by the increasing number of antigen-positive sites. These results suggested that the examination of the Chlamydia trachomatis antigen in the uterine cervix alone is insufficient, to determine the true actual prevalence of the organism.