Abstract-Cadmium kinetics were studied in cadmium-adapted and nonadapted field populations of the midge Chironomus riparius. Accumulation and elimination experiments were carried out using first-generation laboratory-reared animals. Differences between populations were, therefore, assumed to have a genetic basis. Larvae were dissected to analyze the guts and the remainder of the larvae separately. First-order one-compartment models were not always successful in describing accumulation processes, probably due to acclimation. No interpopulation differences were observed in larval development based on dry weights, whereas some differences existed based on pupation rate. In most cases more than 80% of the total amount of cadmium was found in the guts of all populations. Larvae from cadmium-adapted populations showed a decreased net accumulation rate as well as higher equilibrium values (15-20%) compared to nonadapted populations. In addition, cadmium excretion efficiency was increased for cadmium-adapted larvae, which was due to an increased elimination rate from the guts. It was concluded that exposure to high cadmium concentrations in the field resulted in populations of C. riparius with an increased storage capability and an increased excretion efficiency, especially regarding the guts.