<p>Spontaneous and stimulated by hypoxic conditions and a complex of mitogens (LPS, PHA, and ConA) production of IL-1β and IL-10 by peripheral blood cells of adult male Wistar rats 2 weeks before and 1 month after sublethal hypoxic exposure was examined to determine their tolerance to oxygen deficiency in a decompression chamber. To analyze spontaneous cytokine production, heparinized blood cells were incubated in culture medium for 1 and 24 h (37°C, 21% O₂ and 5% CO₂). To study cytokine production stimulated by hypoxia, heparinized blood cells were incubated in culture medium for 1 h (37°C, 1% O₂ and 5% CO₂), and cytokine production stimulated by a complex of mitogens was analyzed by incubating heparinized blood cells in medium supplemented with LPS, PHA, and ConA for 24 h (37°C, 21% O₂ and 5% CO₂). The levels of proinflammatory cytokine IL-1β and anti-inflammatory cytokine IL-10 in a culture medium were measured by ELISA. The response to hypoxic stimulation and exposure to complex mitogen after sublethal hypoxic exposure in the decompression chamber differs from that before it in high (HR) and low resistant (LR) to hypoxia animals. After hypoxic stimulation and exposure to complex mitogen, the production of proinflammatory cytokine IL-1β increases in both HR and LR rats, but the production of anti-inflammatory IL-10 decreases in LR animals and does not change in HR rats. This indicates the formation of a proinflammatory phenotype in LR animals after sublethal hypoxic exposure. The obtained data should be taken into account when conducting studies using animals with different tolerance to hypoxia.</p>