Rat red blood cells were exposed to the Earth’s magnetic field and an attenuated magnetic field, in the presence of tert-butyl hydroperoxide used as an inducer of 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 being released throughout erythrocyte hemolysis. Concentration of reactive oxygen species was determined in samples by spin trapping using electron paramagnetic resonance. It was found that after 4-hour incubation at high tert-butyl hydroperoxide concentrations (>700 μM), red blood cells, which were exposed to an attenuated magnetic field, released considerably more ( p < 0.05) hemoglobin, mostly methemoglobin. After 24-hour incubation at low tert-butyl hydroperoxide concentrations (≤ 350 μM), erythrocytes, which 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 reactive oxygen species concentrations can neutralize attenuated magnetic field effects..