Diagnosis of malaria tertiana is not uncommonly missed or delayed because of a long incubation period, relapses after an unnoticed primary attack or due to suppressed parasitemia under antibiotics or antimalarials. The presently available rapid tests are not suitable for diagnosis of malaria tertiana. Malaria tertiana acquired in Southeast Asia carries a considerable risk of resistance to chloroquine. In this situation mefloquine is used in first place at total dose of 1000-1500 mg. Relapse of malaria tertiana even after primaquine have been described in travellers returning from the tropics. The efficacy of primaquine can be improved by raising the dose. Hereby an increased risk of hemolysis in concomitant glucose-6-phosphate-dehydrogenase deficiency and, more commonly, gastrointestinal side effects have to be considered.