Abstract: An investigation was performed to determine the possible role of metabolism in two resistant strains to thiomethoxam and profenofos by whitefly Bemisia tabaci. Selective synergists were used to study the involvement of hydrolytic or oxidative enzymes in the resistance mechanism of the resistant strains. Resistance level was decreased markedly when DEF (S,S,S-tributyl phosphotithioate) synergized thiamethoxam, suggesting the involvement of increased detoxication by esterases as a part of resistance mechanism. In addition thiamethoxam was synergized moderately when mixed with 25 ppm from TCP (tricresylphosphate) confirming the role of nonspecific esterases in thiamethoxam resistance. Piperonyl Butoxide (PB) synergized profenofos toxicity in resistant strain especially when profenofos mixed with 50 ppm PB which gave synergistic ratio 24.08. The role of diethylmaleate (DM) as inhibitor for glutathione transferases was clear in the case of profenofos resistant strain. However, it exhibited slightly synergistic action in the case of thiomethoxam resistant strain.