[en] The new method for the investigation of fast isotope exchange has been elaborated. It includes combination of two procedures: (1) isotope exchange study without analytical separation of the components (electrical and diaphragm exchange methods) (2) method of constant velocity supply of the radioactively labelled component into the exchange system. The paper presents the derivation and analysis of correlations. The possibilities of the methods are discussed. The new correlations useful for investigation of isotope exchange, using non-separation methods combined with the constant velocity supply method have been derived. These correlations can advantageously be used for the investigation of slow and fast exchange reactions (for the latter the half-time of exchange should be in the order of seconds). The method enables also accurate determination of the exchange time. (T.G.)