In the present work, the recorded kinetics of chemiluminescence enhanced by coumarin 334 indicated that the complexes of cytochrome c with anionic lipids (Cyt-AL), such as cardiolipin (CL) and phosphatidic acid (PA), when added to mitochondrial and cytoplasmic membranes, are capable of catalysing the reactions of lipid free radical formation. The effect of Cyt-CL complex was studied on mitochondria isolated from the liv-er of male Wistar rats and male outbred mice, as well as on erythrocytes isolated from the blood of male Wistar rats. It was shown that Cyt-PA complex exerts a peroxidase effect similar to that of Cyt-CL. Upon exposure to Cyt-CL, the formation of free radicais was more prominent in damaged mitochondria (mitochondria shocked by freeze-thawing and washed by several precipitation-resuspension cycles) than in intact mitochondria. This suggests that Cyt-CL does not pass through biological membranes: even if it penetrates into them, it probably gets stuck in the phospholipid bilayer. Thus, the previously discovered cytotoxic effect of Cyt-CL on câncer cells most likely can be attributed to peroxidation of the cytoplasmic membrane but not of the inner membrane of mitochondria.