The titration of C. trachomatis antibodies (IgG, IgM and IgA) in sera obtained from antigen positive 220 men and 56 women, and antigen negative 384 men and 170 women was carried out by the method of microplate immunofluorescence antibody (MFA). Positive rates of the three class antibodies in antigen positive women were meaningfully higher than those in antigen positive men. Average IgG titer in antigen positive women was significantly higher than that in antigen positive men. Identical result was also obtained, when IgG titers were compared for sera collected from 93 couples.