We compared the sensitivity of two photochemiluminescent methods and used the xanthine-xanthine oxidase assay for superoxide dismutase determination in neutrophils of healthy volunteers. 1U of SOD activity is defined according to McCord and Fridovich as the enzyme activity causing 50% inhibition of the test reaction. 1UPCL was equal to 17.6 ng SOD (2990 U/mg prot., Sigma, Chemicals CO., USA) in the riboflavin-lucigenin photochemiluminescent method. The coefficient of intraserial variability is 2.2% and the coefficient of interserial variability is below 5%. For the same standard SOD in the l uminol photochemilumines- cent method 1U was equal to 252 ng and for the xanthine-xanthine oxidase assay 1U was equal to 287 ng. We found a positive correlation between the riboflavin-lucigenin photochemiluminescent method and the xanthine-xan- thine oxidase assay (r = 0.726, p < 0.0001, n = 21). The riboflavin-lucigenin photochemiluminescent method is more sensitive and specific (eliminats the influence of interferring compounds), and suitable for the determination of SOD in neutrophils as well as in other biological material.

        Key words: superoxide dismutase, photochemiluminescence, luminol, lucigenin.