Aedes albopictus collected from urban districts of China (12 strains) has developed high levels of DDT resistance, while 2 strains collected from rural areas remain susceptible. The mechanism of DDT resistance was due to intensified activity of DDT-dehydrochlorinase, but the penetration of DDT into the mosquito body is also different. This may possibly have had some influence on the resistance levels of some strains, but it seems unlikely that was the main mechanism of DDT resistance.