Laser-excited fluorescence spectroscopy was adopted for dityrosine detection in horse spleen apoferritin. Dityrosine was identified in horse spleen apoferritin. Fractionation of acid-hydrolyzed horse spleen apoferritin showed fluorescence attributed to dityrosine, and other compounds, excited by 325-nm laser radiation. The other fluorescent compounds resulted in a broad fluorescence emission spectrum of horse spleen apoferritin. The broad emission band overlapped with the fluorescence emission spectrum of pure dityrosine. Fractionation of horse spleen apoferritin acid hydrolysate prior to laser-excited fluorescence detection was necessary for dityrosine quantitative analysis. The concentration of dityrosine in horse spleen apoferritin was 2.5% (mol/mol), estimated from the method of standard addition.