The possibility of using EDTA as a masking agent for copper in the photometric determination of nickel by the dimethyglyoxime method has been inveatigate3. It is found that (1) neither the color of the nickel nor that of the copper complex can be formed if EDTA is added before the dimethyglyoxime reagent. (2) If FDTA is added ;after the color ha.s been developed, the nickel complex remains unchanged while the copper complex is destroyed; but in strong alkaline solution, the dimethylglyoxime-copper complex appears to be more stable, and cannot be completely destroyed by EDTA.