The minimum energy path for the reaction of SH with O-3 was investigated at a highly correlated level of calculation using the multireference MP2 and configuration interaction (CI) methods, with basis sets ranging from DZP to aug-cc-pVTZ. Starting from ground state reactants and following the minimum energy path, ground state products and a significant activation energy barrier are obtained. This energy barrier led to a kinetic constant of 2.3 x 10(-17) cm(3)/molecule s for atmospheric conditions of 1 atm and 298 K. These results contrast with experimental findings of the formation of an excited HSO molecule and a kinetic constant several orders of magnitude greater. Since no electronic crossing was also verified in our calculations, these results are suggestive that the experimental kinetic determination might be involving reactants in their excited states, probably O-3.