A procedure has been described for the quantitative determination of copper and iron in one serum sample. The sera are wet ashed to destroy organic material, leaving inorganic salts available in the residue for the subsequent spectrophotometric determination of iron as the ferrous-1,10-phenanthroline complex in the aqueous phase, and copper as the cuprous-2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline in an organic extract phase.