Free radical scavenging and antioxidant activities of metabolites produced by carotenogenic yeasts of Rhodotorula sp. and Sporobolomyces sp. grown under heavy metal presence were studied using various EPR experiments. The thermally initiated decomposition of K(2)S(2)O(8) coupled with EPR spin trapping was shown to be the best choice to characterize antioxidant properties of yeast's samples. EPR spectroscopy revealed that yeast walls showed higher ability to scavenge free radicals than those from inside the cells. Since carotenogenic yeast differ to each other in resistance against the heavy metals due to their individual protective system, quenching properties and antioxidant activities of carotenogenic yeasts were modulated by Ni(2+) or Zn(2+) ions variously.