The oxidn. of HNO2 with H2O2 to HNO3 in aq. HCI solns. was described as a third order reaction. The reaction rate const., was found to be a function of ionic strength (1) and temp. The preexponential factor, k(0), was 9.4. 10(10) I-2/(mol(2) x s) (for I = 0 mol/l) and increased with increasing I according to the equation k=k(0) (1 + 5.3 I). The activation energy was 41.7 kJ/mol.