Five regimens for the radical treatment of falciparum malaria were compared in five geographically separate areas of Thailand. The cure rate for sulfadoxine-pyrimethamine was found to be low in the area of the Kampuchean border and in the northeastern and western parts of the country. This distribution may be related to the spread of resistant parasites through the migration of labourers. A 7-day course of quinine was found to be uniformly effective, with an overall cure rate of 90% in these primary infections with comparatively low parasitaemia.