Two genetically modified enzymes, galactose dehydrogenase and lactate dehydrogenase carrying polyhistidine tails, were used to develop a simple method for quantitation of transition metals. The samples containing copper, nickel or zinc were initially adsorbed to Chelating Sepharose. Excess of engineered enzyme was added and allowed to bind to the chelated metal ions via their additional histidine tails. The amount of metal ions could be determined by addition of enzyme substrate. The detection limits for copper and zinc were 0.01 μmole and 0.2 μmole, respectively.