Artemisinin and its derivatives, dihydroartemisinin and sodium artesunate, enhanced DNA synthesis of mouse spleen cells that had been activated with alloantigens or T cell mitogen Con A, but not B cell mitogen LPS, both in vitro and ex vivo. In vivo experiments showed that DTH response and antibody response against sheep erythrocytes were augmented in sodium artesunate-treated animals. In addition, sodium artesunate, a representative of these compounds, increased IL-2 production from mouse splenocytes stimulated with Con A. Because of the long-term T cell function deficiency in mice after bone marrow transplantation, the effect of sodium artesunate on the immune reconstitution was assessed. The results demonstrated that 10 mg/kg sodium artesunate significantly accelerated the immune reconstitution in mice after syngeneic bone marrow transplantation. These data suggested that artemisinin and its derivatives appeared to promote T cell function selectively, and these compounds had a potential application for the recovery of immune function.