In connection with the state policy focused on import substitution, import-substituting medical products, including reagents for in vitro diagnostics (IVD) are becoming more urgent. Import-substituting medical product is supposed to replace the imported one, therefore products must be interchangeable. However, government medical device market regulation does not provide unified and exhaustive definition of the term «interchangeability». Moreover, state register, stipulated by the Law RF 323-FZ, is not operational due to legal issues with term «interchangeability» and lack of methodology and established procedures of defining interchangeable products, thus, decision of interchangeability falls on medical facilities. Decision of original reagents interchanging for open IVD systems should be taken with regard to analytical, technical and legal aspects. Analytical aspect implies analyzer and reagents are being used only in combination as an analytical system (AS), described by the state standard GOST 53133.1-2008 as «aggregate of devices (including software), calibrators, reagents and consumables, needed for analyte measurements». The most important feature of AS is a result validity, which can be guaranteed only if the analyzer is used with the appropriate reagents and calibrators. In accordance with the industry standard OST 91500.13.001-2003, the first and second stages of quality control should be performed when reagents being changed, which requires control materials significant consumption, as well as being time and labor consuming. Technical aspect implies reagent-analyzer compatibility, recalibration and reprogramming of analyzer, as well as physicochemical interaction between reagents and analyzer system elements. The main priority for medical facilities is to deliver quality healthcare, therefore interchangeable reagents can be used only if the quality of diagnostic is assured. Currently, there are no regulatory documents forbidding end-users to purchase original reagents for IVD or obliging them to purchase import substituted reagents.. Purchase of original reagents is prescribed by Law RF 323-FZ and is not bounded by Law RF 44-FZ. Buyer should be careful purchasing substituted reagents to avoid acquiring of faked, counterfeit and defective good. The registration certificate for substitutional reagents does not define these reagents to be interchanged with original ones and compatible with proper analyzers.