There are two stages in the life circle of Plasmodium spp in humans: exoerythrocytic and erythrocytic stages. Hydroxychloroquine is the major chemotherapeutic agent against malarial parasites in their erythrocytic stage. The recurrence of Plasmodium vivax malaria, which is usually caused by an inadequate treatment or the presence of drug resistant parasites, has been reported frequently in the world, but rarely in Korea. We experienced two patients who recurred with P. vivax malaria after hydroxychloroquine therapy, and treating with insufficient doses of the drug was suspected as the cause of the recurrence. (Korean J Clin Microbiol 2005;8(2):185-188)