A method for qualitative determination of cytochromes of the wild-type and mutant strains of Chalmydomonas reinhardii was developed. The effect of different techniques of cell disruption (ultrasound, Triton X-100, acetone, etc) on detection of cytochrome maxima in the oxidized minus reduced difference spectra was studied on a comparative basis. The development of the stable difference spectrum of the disrupted cell suspension was shown to be a function of incubation time in the presence of an oxidizing or a reducing agent. Cytochromes of the wild-type and 10 nonphotosynthesizing mutants were determined. Four mutants with lesions in cytochromes B559 and C553 were detected. Mutants with lesions in the reaction center of photosystem 2 were found to have a substantially reduced content of cytochrome B559, whereas those with normal photosystems--of cytochrome C553.