The comparative susceptibility to dengue serotype 1, 2 and 4 viruses infection of 9 geographic strains of Azdes albopictus was studied by means of experimental feeding the mosquitoes on pledgets soaked with virus-erythrocyte suspension and intrathoracic inoculation with dengue viruses. Variation in susceptibility for both dengue serotypes 1 and 2 was found among the geographic strains by feeding, but no significant difference among those by intrathoracic inoculation. It was evident that a "gut barrier" was involved. Thresholds of oral infection were not the same for dengue serotypes 1, 2 and 4. In terms of infection rate, Haikou strain was more susceptible to all three serotypes of viruses; Beijing and Chengdu strains were more susceptible to serotypes 1 and 2, respectively. All the geographic strains were more susceptible to dengue serotype 2 comparing with other two serotypes. The mosquito head squash method for demonstrating dengue virus antigen by indirect fluorescent antibody technique was modified by mosquito brain tissue smear. This would be more accurate in detecting the dengue virus antigen in the brain tissue.