We have previously reported (Kurane et al., Arch. Virol. 110, 91-101, 1990) that human T cell leukemia and lymphoma cell lines could be infected with dengue virus. In the present study we examined whether human T lymphocytes which are not leukemia or lymphoma cells can be infected with dengue virus. Dengue virus-specific human CD4+ T cell clones, JK44 and JK49, and CD8+ T cell clones, CB2.8 and CB6.17, were infected with dengue-2 virus. Dengue virus antigen-positive cells were detected in each of the four T cell lines by the immunofluorescence staining 20-60 hrs post infection (p.i). Infectious dengue virus was detected in the culture fluids 40 hrs p.i. These results demonstrate that activated CD4+ and CD8+ human T lymphocytes can be infected with dengue-2 virus.