The effect of sodium nitrite (NaNO2) (0.07–3.50 mM) and sodium selenite (10 µM) on the oxidation of hemoglobin (Hb) and lipid peroxidation (LPO) in human red blood cells in vitro is examined. It was revealed that nitrites have a significant effect on oxidative processes in Hb and to a lesser extent in erythrocytes, and sodium selenite weakens the development of the nitrite-induced oxidative process in erythrocytes and reduces the formation of methemoglobin (MetHb) by 12–25%. Having a significant effect on the oxidative modification of Hb, nitrites at moderate concentrations do not lead to a noticeable increase in lipid peroxidation in erythrocytes. Under the influence of high NaNO2 concentrations (3.50 mM), an increase in the accumulation level of MetHb by ten leads to an increase in the accumulation of thiobarbituric acid (TBA) active products by 40–70%. If at a low final concentration of nitrite (0.07 mM) there is no noticeable change in the content of total membrane-bound hemoglobin (oxyHb and MetHb), then at a moderate (0.70 mM) and high (3.50 mM) concentration these changes are obvious 10 and 15%, respectively. Introduced into the incubation medium before and after incubation with nitrite, sodium selenite with concentration 10 μM has a certain inhibitory effect on this process.