Mefloquine, a quinolinemethanol antimalarial, is effective single dose therapy for all species of malaria infecting humans, including multi-drug-resistantPlasmodium falciparum.It is used both in prophylaxis and treatment. Mefloquine is available either as the hydrochloride salt alone, or in a combined preparation with sulfadoxine and pyrimethamine. There is no parenteral formulation. Several assay methodologies have been developed, but high performance liquid chromatography has been the most used in recent pharmacokinetic studies. These have shown in healthy volunteers that mefloquine is absorbed with a half-life of 1 to 4 hours and a time to peak concentration of 7 to 24 hours (median 16.7 hours). Mean peak blood concentrations have ranged between 50 and 110 (median 83) ng/ml/mg/kg. Estimates of total apparent volume of distribution (Vd/f) have ranged from 13.3 to 40.9 (median 19.2) L/kg, systemic clearance (CL/f) from 0.022 to 0.073 L/h/kg (median 0.026 L/h/kg), and terminal elimination half-life from 13.8 to 40.9 days (median 20 days). Systemic clearance appears to be increased in late pregnancy. In uncomplicated falciparum malaria, peak blood concentrations are 2 to 3 times higher than those in healthy subjects ranging from 112 to 209 (median 144) ng/ml/mg/kg because of contraction in the total apparent volume of distribution. Systemic clearance is usually reduced but elimination rates are increased (possibly because of reduced enterohepatic recycling). Mefloquine absorption appears to be reduced in severe falciparum malaria; plasma protein binding exceeds 98% in both healthy subjects and patients. No important drug interactions have been identified as yet, but the potential for serious interactions with quinine has not been adequately investigated. More studies are needed on the disposition of mefloquine in children.