A spectrophotometric method for determination of trace amounts of cadmium and zinc in waste water with PAR and mixed ionic and non-ionic surfactants is described. The interferences of foreign ions can be eliminated by masking with a mixture of triethanolamine, potassium fluoride, ethylenediamine and sodium hexametaphosphate. By virtue of the difference between the absorbances before and after addition of a little sodium diethyldithiocarbamate, cadmium and zinc can be determined directly in aqueous solution without separation. Beer's law is obeyed for 0-20 microg of Cd or 0-12 microg of Zn in 25 ml of solution. The apparent molar absorptivities at 505 nm are 8.65 x 10(4) l.mole(-1).cm(-1) for Cd and 8.21 x 10(4) l.mole(-1).cm(-1) for Zn. Results obtained by applying the proposed method to waste-water samples agree well with those obtained by atomic-absorption spectrophotometry.