Abstract—Red blood cells of rats were exposed to the earth’s magnetic field and an attenuated magnetic field in the presence of tert-butyl hydroperoxide to induce oxidative stress. Spectral analysis within the wavelength range of 500–700 nm was used to estimate the concentration of three forms of hemoglobin: oxyhemoglobin, methemoglobin, and hemichrome, released during erythrocyte hemolysis. The concentration of reactive oxygen species was determined in samples by spin trapping using electron paramagnetic resonance. It was found that after 4 h of incubation at high tert-butyl hydroperoxide concentrations (>700 μM), red blood cells that were exposed to an attenuated magnetic field released considerably more (p < 0.05) hemoglobin, mostly methemoglobin. After 24 h of incubation at low tert-butyl hydroperoxide concentrations (≤350 μM), erythrocytes that were exposed to the earth’s magnetic field released relatively more (p < 0.001) hemoglobin, with methemoglobin as a major form of total hemoglobin. Red blood cells exposed to the attenuated magnetic field generated more oxygen radicals than cells exposed to the earth’s magnetic field. Under certain oxidative stress conditions, the attenuated magnetic field can impair the functional state of red blood cells and provoke cell death. However, low concentrations of reactive oxygen species can neutralize attenuated magnetic field effects.