Introduction Sarcoidosis is a granulomatous disease of unknown etiology. The role of serum immunoglobulins in the development of the disease is not completely clear, perhaps their participation is in the formation of granuloma by attachment to immune complexes (IC). The aim of the study was to reveal the specific features of the formation of specific immune complexes of IgG and IgE isotypes in patients with sarcoidosis and pulmonary tuberculosis. Material and methods During the period from January to July 2017, a prospective scientific research within the framework of Megagrant with a set of patients with newly diagnosed disseminated processes in the lungs aged 18 to 65 years is conducted at "SPb NIIF" of the Ministry of Health of the Russian Federation and St. Petersburg State Medical University. Exclusion criteria were data on the use of immunosuppressive methods of treatment, taking anti-tuberculosis therapy, conducting a course of plasmapheresis for less than 2 months from the time of inclusion, the presence of HIV infection, syphilis, tumors, diabetes mellitus in decompensation, and the identification of other granulomatosis. The inclusion criterion corresponded to 89 patients (47 men and 42 women, average age 38.5 ± 9.57 years). Based on the results of the examination, the patients were divided into two groups: Group I (n = 56) of patients with verified diagnosis of respiratory tuberculosis; II group (n = 33 patients) with sarcoidosis of the lungs of the 2nd stage. The control group consisted of 19 healthy donors. All patients underwent examination including a clinical examination, spiral computed tomography of the chest, setting up a Mantoux sample with 2TE and a test with Diaskintest, bacteriological examination of sputum on MWT, histological examination of lung tissue, including molecular genetic research. In FGBU "Petersburg Institute of Nuclear Physics. B.P. Konstantinova ", a study of blood plasma samples of patients was carried out using the method of dynamic light scattering with the addition of ESAT-6 and SFP-10 in vitro. Statistical processing was carried out using the program Statistica 7.0. Differences between groups were considered significant at a level of p <0.05. Results. Formation of IRs formed with the addition of a specific antigen was registered in 100% (56) cases in the I group of patients with tuberculosis, the formation of immune complexes was recorded (total IR - 6.85 ± 0.37, IgG1 - 4.25 ± 0.26; IgG3 - 3.2 ± 0.16, IgE - 3.29 ± 0.25, IgG1 + IgG3 - 3.83 ± 0.28, IgG1 + IgE - 5.66 ± 0.55, IgG3 + IgE - 2, 86 ± 0.5). The greatest contribution to the scattering was registered in IgG1 + IgE immunoglobulins. In 100% (33) of cases with sarcoidosis and 19 (100%) of healthy donors, the formation of immune complexes was not recorded. Differences are significant (p = 0.000 ...) when comparing group I and group II, and when comparing results with healthy donors. The diagnostic specificity of the results was 100%. Conclusions The significant differences in the formation of specific immune complexes with the addition of a specific antigen to the blood plasma of patients with tuberculosis and respiratory sarcoidosis can serve as an additional criterion for differential diagnosis of tuberculosis and sarcoidosis.