Epidemics of dengue type 1 infection were studied in Nauru, Ponape, and Fiji and epidemics of dengue type 2 in Tonga and Tahiti. The nature of the antibody response (primary or secondary) was studied in selected cases of severe hemorrhagic dengue or dengue shock syndrome on Pacific islands and in Southeast Asia. Mosquito inoculation was compared with conventional cell culture techniques for the isolation of dengue viruses from patients with dengue hemorrhagic fever in Bangkok.