Selective UV-spectrophotometric methods for determination of iron(III) in iron(II) samples have been developed. The methods are based on the interaction of Fe(III) with quercetin and morin, compounds of the flavonoid group. Redox reactions occurring between Fe(III) ions and the reagents used make the basis for the detection. Iron(II) does not react with quercetin and morin under the conditions applied aqueous-methanolic (3:2) soluions, 0.3 mol L-1 HCl, 1.2 x 10-4 mol L-1 quercetin (morin) and does not interfere with the determination of Fe(III). Iron(III) can be determined up to 15 μg mL-1 using both the examined systems. The detection limits are 0.06 and 0.38 μg mL-1 when using quercetin or morin, respectively. The method with quercetin was applied to the determination of Fe(III) (ca. 0.2%) in a Fe(II) pharmaceutical product. U radu je opisan razvoj selektivnih UV-spektrofotometrijskih metoda za određivanje željeza(III) u uzorcima željeza(II). Metode se temelje na redoks reakciji Fe(III) sa spojevima iz skupine flavonoida -- kvercetinom i morinom u reakcijskim uvjetima u kojima željezo(II) ne reagira (vodeno/metanolna otopina 3:2, 0,3 mol L-1 HCl, 1,2 x 10-4 mol L-1 kvercetin ili morin). Najniža koncentracija željeza(III) koja se može odrediti u oba ispitivana sustava je 15 μg mL-1. Granice detekcije su 0,06 i 0,38 μg mL-1 ako se koristi kvercetin odnosno morfin. Metoda s kvercetinom primijenjena je za određivanje Fe(III (približno 0,2%) u farmaceutskom proizvodu Fe(II).