The pathways for the reaction between methylperoxy (CH3O2) and bromine monoxide (BrO) radicals have been examined by using the quadratic configuration interaction method. It is found that the most feasible pathway of the CH3O2+BrO reaction is the formation of CH3OOOBr as an intermediate during the reaction and its dissociation into CH2O and HOOBr. This study finds that besides CH3OOOBr, CH3OOBrO may also exist as an intermediate complex during the CH3O2+BrO reaction. (C) 2003 American Institute of Physics.