The nucleophilic substitution reaction of p-nitrophenyl diphenyl phosphate, p-nitrophenyl p-toluene sulfonate and insecticide fenitrothion with pralidoxime have been studied at 27 A degrees C in the presence of different cationic surfactants. Micellar rate enhancements increase as the cationic head group is made less polar. The order of cleavage of different electrophilic centres by pralidoxime is P = O > S = O > P = S.