30 pairs of patients with complicated Plasmodium falciparum malaria (with anaemia, hyperpyrexia, jaundice or more than 5% of erythrocytes parasitized) were studied. Patients with cerebral signs and symptoms were excluded. One group of patients was treated with oral mefloquine (750 mg) and artemether (600 mg by injection, 200 mg initially and 100 mg every 12 h). The second group of patients was treated with quinine (10 mg/kg orally every 8 h for 7 d). All patients were admitted to hospital for 7 d and examined subsequently on days 14, 21 and 28. All those treated with mefloquine plus artemether survived and their parasite clearance time and fever clearance time were significantly shorter than those of patients receiving quinine. 2 patients treated with quinine died. There was no recrudescence in any patient of either group.