An improved method for the isolation and identification of dengue viruses is described. Viruses were isolated in mosquito cell cultures (C6/36 or AP-61), identified by indirect fluorescent antibody technique, and typed by complement-fixation test, using the cell culture fluid as antigen. The sensitivity of this method was compared with mosquito inoculation in comparative titrations of 16 low passage dengue virus strains. Although lower virus titers were obtained by the mosquito cell culture technique, its decreased sensitivity was compensated for by the much larger volume (588X) which could be assayed. By incubating the mosquito cells at 32 degrees C, dengue viruses can be identified and typed within 6 days after inoculation.