In this paper the absorption spectra of the copper complex with cyanide ion have been studied by conventional and derivative spectrophotometry. The use of third-derivative spectra both eliminates the interference from other metals and improves the sensitivity. Beer's law is obeyed for 0.64–3.2 μg/ml of copper. The relative standard deviation for 7 determinations 1.5 μg/ml of copper was 0.78%. The detection limit, corresponding to a signal-to-noise ratio of 2, was found to be 0.15 μg/ml. The suggested method has been applied successfully to the analysis of some iron alloys and aluminium alloys without any separation.