A new method for determining microquantities of zinc using o-nitrosophenol as reagent is described. The prepararion of the reagent in the laboratory is also described, because it is not available for sale. The formed complex, after additional pyridine, can be extracted with organic solvent (toluene) and zinc can be determined spectrophotometrically by measuring the absor-bance of the organic layer at 482 nm. The optimum range of concentration was found to be 0.04 μg to 0.8 μg/ml in the final dilution. By masking zinc using cyanide and thiosulphate and selective demasking by the addition of hydrated chloral, Zn can also be determined in the presence of larger amounts of interferences.