Detoxifying enzymes and susceptibility to three insecticides ofApanteles plutellaeKurdj andDiadegma semiclausumHellen, parasitoids of diamondback moth larvae, were determined. Both insects were susceptible to malathion and methyl parathion and were considerably tolerant to fenvalerate. Although the attempt to correlate this susceptibility with the detoxication capabilities, in terms of activities toward model substrates of carboxylesterase, glutathione S-transferase, and microsomal monooxygenase, of these two parositoids was unsuccessful, the possibility of using this means to assess the potential for development of insecticide resistance in natural enemies is discussed.