Effects of hemoglobin concentration (Hb), pH, and body temperature (T) on the relationships between ΔlogPO2/ΔT and PO2 were studied by means of a mathematical model using a Newton-Raphson iteration method. The functions between ΔlogPO2/ΔT and PO2 were affected by the above three factors. New equations considering the effects of Hb, pH, and T were proposed by modifying the equation reported by Severinghaus: ΔlogPO2/ΔT=(L+(U-L)/(A(vPO237)B+1))(10-2) where U=3.15-0.45(7.4-pH37) L=0.68-0.09(7.4-pH37) A=5.86(exp10(0.074(T)-0.294(7.4-pH37)-11))((Hb)0.913) B=6.33(exp10(-0.0051(T)))((Hb)-0.113)+0.24(7.4-pH37) and vPO237 is virtual PO237 which may exist when PO237 is corrected to standard conditions (pH=7.4, BE=0) by the following equations: vPO237=PO237(exp10(fB(7.4-Ph37)-0.0013(BE))) fB=(PO237/26.6)0.08-1.52 where fB is the Bohr factor. The above equations provided values of ΔlogPO2/ΔT which fit closely to those obtained by the complex iteration method with maximum differences of less than 1.3×10-3 at T=27, indicating that maximum % errors for PO2 at T (PO2T) are less than 3.0% at T=27 and that our equations can be applied over a wide range of Hb, Ph37 and T.