Laboratory experiments investigated the comparative degradation of five carbamate insecticides in soil as affected by enhanced microbial degradation. Soils with prior field exposure to carbofuran, cloethocarb, or several carbamates contained adapted microbial populations capable of rapidly degrading carbofuran. Bendiocarb was rapidly degraded in all soils displaying enhanced carbofuran degradation, but carbaryl and cloethocarb were most rapidly degraded only in soil with prior exposure to several carbamates or to cloethocarb. The persistence of aldicarb and its oxidative metabolites aldicarb sulfoxide and aldicarb sulfone was not dramatically altered in soils with enhanced carbofuran degradation. Results indicate that although cross-adaptations for enhanced degradation exist within the carbamate insecticide class, structural similarity may play a role in modifying the expression of enhanced degradation in soil.