[en] Ruthenium(III) and platinum(IV) form 1:2 (metal:ligand) complexes with acenaphthenequinone mono(thiosemicarbazone)(AQTS). The complexes are soluble in 70 % N,N-dimethylformamide (DMF). The reagent has been used for the spectrophotometric determination of Ru(III) and Pt(IV). The optimum ranges of concentration for the determination of Ru(III) and Pt(IV) are 2.02 - 7.09 and 2.83 - 11.6 ppm over the pH range 5.3 - 6.8 and 1.9 - 4.1, respectively. The Sandell sensitivities for the determination of Ru(III) and Pt(IV) are 0.01 and 0.016 μg cm^-2, respectively. The determination has also been carried out in the presence of foreign ions. (author)