ECM is widely used in the production of gas turbine engines with high demands to the quality and accuracy of the details. Performance, accuracy and quality of the ECM are largely determined by the stability of the electrolyte composition and its parameters during processing. One important parameter is the hexavalent chromium content in the electrolyte, which is important from an environmental point of view. During the machining of material the dissolving alloy generates compounds of trivalent and hexavalent chromium depending on the alloy composition and the electrolyte type. Thus such compounds are redistributed between the electrolyte and sludge sediment.  The dynamics of chromium compounds accumulation in the electrolyte at ECM of EI 893 – nickel based and EI 612 - the iron-nickel based superalloys was studied. The physico-chemical parameters of the electrolyte depending on changes in its composition were recorded simultaneously with.   The sludge accumulation in the electrolyte was carried out using the laboratory equipment simulating conditions ECM (maintaining small interelectrode gaps sufficiently high operating current density, the electrolyte circulating feed mode while stabilizing its temperature by a heat exchanger).  Electrolyte volume was strongly controlled to avoid losses in order to increase the accuracy of its composition determination. Dissolution of the sample was carried at a current density of 2 A/cm2 for a certain time. Then the amount of dissolved metal was determined, sampling for chemical analysis of the electrolyte at the moment was done and the product concentration in the electrolyte was determined. Determination of chromium, nickel and iron concentration was carried out separately for the precipitate and the filtered solution.. We calculated the dissolution rate of the alloy and made allowances for the remaining amount of electrolyte. The procedure is repeated until a substantial electrolyte contamination (comparable to service contamination).  Anodic dissolution of the alloys varies depending on the alloy composition and the electrolyte type. In the nitrate electrolytes dissolved chromium exist into solution predominantly in the hexavalent form, and chlorides - trivalent. Steel EI 612 in the mixed nitrate and nitrate-chloride electrolytes dissolves with a variable current efficiency. EI 893 alloy dissolves with essentially the same high speed regardless of the composition of the electrolyte. In all cases ECM of the alloys occurs with increasing accumulation of hexavalent chromium in the solution, while the trivalent chromium is present only in the precipitate.    Accumulation of hexavalent chromium in the solution and the precipitate depends on the sorbent ability of the sludge, consisting almost entirely of nickel hydroxide or a mixture of hydroxides of nickel and iron. However, the resulting sludge is insufficient for the full adsorption of chromium dissolved and remains in solution. A characteristic feature of ECM of the iron containing alloy in the nitrate or mixed electrolyte, unlike the alloy EI 893, is the preferential accumulation of CrVI in the solution (at a similar ratio of trivalent and hexavalent chromium compound amounts). The reason for this behavior on the iron-nickel alloy can be high oxidizing ability in nitrate solution formed Fe+2 and transfer of the dissolving chromium in the hexavalent state. In this case sludge as sorbing agent is insufficient to hold the dichromate ions, and they go into solution.  This work was supported by the Academy of Sciences of Moldova (project 15.817.02.05.A)