The pharmacokinetics of quinine were studied in six Nigerian patients during acute uncomplicated falciparum malaria and convalescent periods. An oral dose of 10 mg/kg quinine dihydrochloride administered 8-hourly for 7 days gave parasite and fever clearance times of 36.0 +/- 16.6 h and 18.0 +/- 6.4 h, respectively. From the individual quinine plasma profiles the mean plasma concentration of quinine at the time of parasite clearance was estimated as 4.5 +/- 1.1 micrograms/ml. Plasma quinine levels during malaria rose rapidly reaching a peak around the second and third days and declining thereafter as patients improved clinically. In acute malaria plasma quinine levels were more than two-fold higher than in convalescence; the mean AUC(0-12) in malaria was 37.9 +/- 14.7 micrograms.h/ml compared to 17.9 +/- 8.5 micrograms.h/ml in convalescence. The apparent oral clearance (CL/F) and volume of distribution (Vd/F) during the acute phase of the malaria (1.9 +/- 0.7 ml/min/kg and 1.8 +/- 0.9 l/kg, respectively) were significantly lower than in convalescence (4.5 +/- 2.1 ml/min/kg and 4.2 +/- 3.2 l/kg). The present data suggest that malaria parasites in African patients are still very sensitive to quinine and that the current dosage of quinine is effective for the treatment of acute falciparum malaria in African patients without augmenting therapy with any other drug such as tetracycline or sulphadoxine-pyrimethamine. It also confirms that malaria significantly alters the pharmacokinetics of quinine in humans.