1. The pharmacokinetics of artemether were investigated (a) in six healthy male Thai volunteers after single 200 mg oral doses and (b) in eight male Thai patients with acute uncomplicated falciparum malaria after an initial 200 mg oral dose followed by 100 mg at 12 h then 100 mg daily for 4 days. 2. In the healthy subjects, median (range) maximum plasma concentrations of artemether of 118 (112-127) ng ml-1 were reached at 3 (1-10) h. Thereafter, drug concentrations declined monoexponentially with a median (range) t1/2.z of 3.1 (1.0-9.6) h. The median (range) AUC and MRT values were 1.10 (0.33-4.44) micrograms ml-1 h and 8.3 (3.5-20.8) h. The median Cmax value of dihydroartemisinin, an active metabolite, was 379 (162-702) mg ml-1 at 6 (2-12) h. Its median AUC value was 6.6 (0.83-38.7) micrograms ml-1 h; the apparent t1/2.z was 10.6 (4.7-19.2) h and the median MRT value was 16.0 (5.0-41.0) h. 3. In the patients, a higher Cmax value of parent drug than those observed in healthy subjects (median and range of 231 (116-411) ng ml-1), was reached at 3 (1-3) h after the first dose. Steady state was reached after the third dose (24 h) and concentrations fluctuated over the range of 36-60 ng ml-1. The respective median (range) values of AUC and t1/2.z were 5.8 (3.76-12.9) micrograms ml-1 h and 4.2 (2.5-5.3) h.(ABSTRACT TRUNCATED AT 250 WORDS)