In some areas clinicians have combined parenteral artesunate and quinine in the belief that the 2 drugs would be additive or synergistic in severe malaria. A randomized comparison of the effectiveness of intravenous (iv) artesunate versus iv artesunate and iv quinine together on parasite clearance was conducted in 1998/99 amongst 69 patients with uncomplicated and severe Plasmodium falciparum malaria in western Thailand. The parasite clearance time did not differ significantly between the 2 treatment groups (P = 0.12), but adverse events were significantly more frequent in the artesunate plus quinine group (P = 0.05). Quinine did not have a significant antipyretic effect and artesunate did not affect the electrocardiographic QTc interval. There is no benefit evident from combining parenteral administration of these 2 antimalarial drugs in the acute phase of treatment.