This paper describes a sensitive method for the determination of ruthenium(III) and palladium(II) in mixtures (up to 16 µg ml–1 of ruthenium and 4.5 µg ml–1 of palladium) by first and second derivative spectrophotometry. The method is based upon the coloured complexes that both ruthenium and palladium form with 2-thiobarbituric acid. A statistical analysis of the experimental results is presented.