Apparent equilibrium constants have been measured for the following biochemical reaction : L-aspartate(aq) + 2-oxoglutarate(aq) = oxaloacetate(aq) + L-glutamate (aq). This reaction, catalysed by aspartate transaminase, alas studied over the ranges 283.15 less than or equal to T/K less than or equal to 303.15, 6.94 less than or equal to pH less than or equal to 7.13, and 0.163 less than or equal to I-m/(mol.kg(-1)) less than or equal to 0.167, where T is temperature and I-m is ionic strength. The instability of the oxaloacetate in solution required the use of an experimental procedure that was brief. Thus, the procedure used was to measure the change in the chromatographic response Delta R of the oxaloacetate chromatographic peak that accompanied the reaction. Values of Delta R were measured for several solutions under near equilibrium conditions. The chromatographic response Delta R is expected to be zero for a solution that is at equilibrium with regard to the above reaction and prior to the addition of the enzyme. The results were used to calculate the standard molar Gibbs energy change Delta(r)G(m)degrees = (4.82 + 0.21) kJ.mol(-1), the equilibrium constant K = (0.143 +/- 0.012), the standard molar enthalpy change Delta(r)H(m)degrees = (1.9 +/-2.9) kJ.mol(-1), and the standard molar entropy change Delta(r)S(m)degrees = -(10 +/- 10) J.K-1.mol(-1) for the following chemical reference reaction at T = 298.15 K and I-m = 0 : L-aspartate(-) (aq) + 2-oxoglutarate(2-) (aq) = oxaloacetate(2-) (aq) + L-glutamate(-) (aq). Under near physiological conditions (T = 311.15 K, pH = 7.0, I-m = 0.25 mol.kg(-1)) the apparent equilibrium constant K＇ for the overall biochemical reaction is calculated to have the value 0.147; the standard transformed Gibbs energy change Delta(r)G(m)＇degrees = 4.96 kJ.mol(-1) under these conditions.