A 22-year-old male student, who had been to Indonesia, was admitted to our hospital because of a high grade fever on October 12, 1990. On admission, vivax malaria parasites were detected in his blood smears and the antibody titers against Plasmodium vivax and P. falciparum antigen were respectively 1: 1024 and 1: 64 by the indirect fluorescent antibody test. Therefore, he was diagnosed as having vivax malaria and was treated with sulfadoxine/pyrimethamine (Fansidar), followed by primaquine at 15mg/day for 14 days. However, relapse occurred twice after treatment with the above-mentioned standard dose of primaquine. After his second relapse, he was treated with primaquine at 22.5mg/day for 14 days and remission was finally achieved without any adverse reactions. The antibody titer against P. vivax did not re-increase during the first and second relapses.
