Relevance. The problem of timely and effective diagnosis of COVID-19 remains one of the main problems facing healthcare. In this regard, the task of developing test systems for the etiological diagnosis of COVID-19 remains extremely relevant. Purpose To develop ELISA test system for detection of G specific immunoglobulins to SARS-COV-2 coronavirus by immunoblotting (Line Blot). Methods. Elaboration of techniques for obtaining test components and preliminary assessment of its diagnostic effectivenessin blood serums from COVID-19 patients treated at N. I. Pirogov First Gradsky Hospital, Moscow, and serums from healthy human donors. Results. The study of 104 blood serum samples from COVID-19 patients and 100 blood serum samples from healthy human donors, pre-tested by ELISA IgG to SARS-CoV-2 using «Vitrotest SARS-CoV-2 IgG» test systems (Vitrotest, Ukraine) and «ELISA-SARS-CoV-2-AB-G» (CJSC EKOlab, Russia) showed high diagnostic efficiency of the new test system. Conclusion. The new test system after state registration of the medical device can be recommended as a confirmatory test for the etiological laboratory diagnosis of COVID-19.