Acute pharmacokinetics of intravenously infused quinine were studied in 25 patients with cerebral malaria and 13 with uncomplicated falciparum malaria. In patients with cerebral malaria receiving the standard dose of 10 mg/kg every eight hours, plasma quinine concentrations consistently exceeded 10 mg/liter, reaching a peak 60 +/- 25 hours (mean +/- 1 S.D.) after treatment was begun and then declining. Quinine total clearances (Cl) and total apparent volumes of distribution (Vd) were significantly lower than in uncomplicated malaria (Cl, 0.92 +/- 0.42 compared with 1.35 +/- 0.6 ml/min/kg, p = 0.03; Vd, 1.18 +/- 0.37 compared with 1.67 +/- 0.34 liter/kg, p = 0.0013). There was no significant difference between the two groups in elimination half-times (t/2) or renal clearances (Cu) (t/2, 18.2 +/- 9.7 compared with 16 +/- 7.0 hours; Cu, 0.21 +/- 0.16 compared with 0.21 +/- 0.08 ml/min/kg). In nine patients studied following recovery, Cl (3.09 +/- 1.18 ml/min), Vd (2.74 +/- 0.47 liter/kg), and Cu (0.53 +/- 0.22 ml/min/kg) were significantly greater (p less than or equal to 0.0004), and t/2 was significantly shorter (11.1 +/- 4.1 hours, p = 0.006) than during the acute illness. Cu accounted for approximately 20 percent of Cl in all groups. Renal failure did not alter the disposition kinetics in cerebral malaria. There was no clinical or electrocardiographic evidence of cardiotoxicity and no permanent neurotoxicity. Quinine toxicity in cerebral malaria has probably been overemphasized. The benefits of high plasma concentrations in the acute phase of this life-threatening disease appear to outweigh the risks, particularly in view of the increasing resistance of Plasmodium falciparum to quinine in Southeast Asia.