A volumetric method for the determination of malathion in emulsifiable concentrates has been developed. The method is based on the alkali cleavage of malathion to give O,O-dimethylphosphorodithioic acid that forms a complex with Bi(III). The complex is extracted with chloroform and the bismuth left uncomplexed is titrated with the disodium salt of ethylenediaminetetraacetic acid. The free O,O-dimethylphosphorodithioic acid that may be present and interfere in the determination is rectified by doing the complex formation without hydrolysing the sample. Hence, the amount of malathion in the sample can be determined.