Highly sensitive diagnostic preparations for the detection of C. trachomatis by direct immunofluorescent and enzyme immunoassay techniques were obtained with the use monoclonal antibodies to C. trachomatis genus-specific polysaccharide antigen. The enzyme immunoassay diagnostic preparation permitted the detection of C. trachomatis in experimental specimens in a dose of 4-14 ng protein. The results of the primary clinical trial of the immunofluorescent preparation revealed that its effectiveness was not lower than that of similar foreign commercial preparations. The use of this diagnosticum for the study of clinical material obtained from 1,603 patients with different venereal diseases showed the presence of chlamydial contamination in 40.2% of the examined patients. The data thus obtained made it possible to recommend the newly developed immunofluorescent preparation for diagnosing infections caused by C. trachomatis.