This study revealed the presence of O-antigen of group D salmonellae and Vi-antigen in circulating immune complexes in patients with typhoid fever, bacteriologically confirmed (56 +/- 5.6% and 65 +/- 5.4% of cases, respectively) and not confirmed (15.5 +/- 5% and 39 +/- 7% of cases, respectively), in patients with diarrhea of nontyphoid etiology in the presence of negative results of the coagglutination test and in healthy persons. The level and dynamics of circulating immune complexes were established with respect to the antigens contained in these complexes. Altogether O- and Vi-antigens were detected in circulating immune complexes, respectively, in 92%, 96% and 94% of cases on weeks 1, 2 and 3 from the beginning of the disease, and in all cases on weeks 4 and 5, the antigens being determined together and separately. Thus, the latent persistence of S. typhi antigens as part of circulating immune complexes in the blood serum was established. The determination of such persistence is of great pathogenetic and diagnostic importance, which also applies to the early period of the disease. The use of such specific and sensitive method as the coagglutination test for this purpose accelerates and facilitates the diagnosis of typhoid fever.