The aim of the study was to investigate the effect of complement on the activity of hemolysin and chlamydial antigen in the complement fixation reaction (CFT). The efficiency of the micromethod CFT for the diagnosis of chlamydia and its higher sensitivity in comparison with the macromethod is shown. Taking this into account, titration of hemolysin is recommended to be carried out in CFT using the macromethod. An inverse relationship was established between the activity of chlamydial antigen and complement, namely, a decrease in antigen activity with an increase in the working complement titer in micro-CSCs, as well as the effect of the complement titer on the activity of hemolytic serum. Established a higher activity of hemolysin when using canned diluted 1:10 complement (1: 1) compared with native (1:20). The optimal dilution of complement 1:20 was determined for titrating hemolysin and ensuring a higher activity of chlamydial antigen in micro-CSCs. Compared with the previously developed method (reaction components, 20 μl each), the induced micro-RSK data indicate the effectiveness of its formulation in a volume of 25 μl components. The data obtained indicate a correlation between the results of complement titration for both methods (domestic, with a single exposure in a water bath at 37 ° C) and the Polish technique (double exposure in a water bath at 37 ° C). On the model of chlamydial antigen, it is possible to draw appropriate conclusions regarding other pathogens (brucellosis, listeriosis, yersiniosis, campylobacteriosis) during serological diagnostics using CFT.