Catalytic antibodies have been studied widely, but little is known about their applicability as therapeutic reagents in vivo. Here we report that carbaryl, a widely used broad-spectrum carbamate insecticide that is toxic to animals and humans, is hydrolyzed by polyclonal catalytic antibodies induced in vivo by a phosphate immunogen. To test the efficacy of the in vivo-induced polyclonal antibodies, we immunized mice with the phosphate immunogen and assayed their sensitivity to carbaryl by determining the ED50 value, the dose that produces lowest-grade tremors in 50% of animals. We found that the ED50 for immunized mice was 43% higher than that for nonimmunized mice and that this increase in ED50 probably resulted from the hydrolysis of carbaryl by the catalytic antibodies in vivo. Our results suggest that polyclonal catalytic antibodies can be used as therapeutic reagents in vivo. (C) 2002 Elsevier Science (USA).