Ab initio calculations using the UMP2 and UQCISD methods with correlation consistent double-zeta and triple-zeta basis sets were applied to study the reactions of HNO with H and OH radicals. The classical energy barrier for the abstraction H + HNO --> H-2 + NO is 0.5 kcal/mol. The reaction path of OH + HNO is: OH + HNO --> HNO(OH)-complex --> TS --> NO(H2O)-complex--> H2O + NO with no energy barrier relative to OH + HNO entrance channel. Canonical and microcanonical variational transition state theory calculations were carried out for these reactions (200-2500 K) and compared with available experimental kinetic data. (C) 2004 Elsevier B.V. All rights reserved.