The reaction of dehydrochlorination of 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane DDT, with hydroxide ions has been studied in aqueous micellar solutions of N-hexadecyl-N,N-dimethyl-3-ammonio-1-propane- sulfonate, SB3-16, in the presence of high and moderately high concentrations of various background electrolytes. The results show that at these concentrations the nature of the anion which comes from the salt is not the only factor influencing reactivity, but the nature of the cation also affects the k(obs) value. This was explained by considering that both the anion and the cation of the added salt bind to the surface of SB3-16 micelles.