The synthetic tripeptide pinealon (Glu-Asp-Arg) demonstrates dose-dependent restriction of reactive oxygen species (ROS) accumulation in cerebellar granule cells, neutrophils, and pheochromocytoma (PC12) cells, induced by oxidative stress stimulated by receptor-dependent or -independent processes. At the same time, pinealon decreases necrotic cell death measured by the propidium iodide test. The protective effect of pinealon is accompanied with a delayed time course of ERK 1/2 activation and modification of the cell cycle. Because restriction of ROS accumulation and cell mortality is saturated at lower concentrations, whereas cell cycle modulation continues at higher concentrations of pinealon, one can conclude that besides its known antioxidant activity, pinealon is able to interact directly with the cell genome.