Abstract: The minimum effective concentration (MEC) of pyronaridine (PND) against Plasmo-, dium falciparum FCC1 was determined by a rabbit/in vitro 48 h assay. It was found that the MEC assayed with dosed rabbit serum was 4.7f331.2 ng/ml, and with control rabbit serum added with PND, 5.2± 2.0 ng/ml. There was no significant difference between the two values (P0.05). Dosage regimen was proposed basing on MEC, and the pharmacokinetic data in malaria patients studied previously. Whole blood MEC, maintenance dose and loading dose were calculated, and the proposed dosage regimens were presented as follows: d1 4 mg/kg, d2 2 mg/kg im: or capsule (or enteric coated tablet), d1 10 mg/kg, d2 5 mg/kg po, while the dosage regimens in current use are 3 mg/kgta × 2, im q6h; or enteric coated tablet, d, 6 mg/kg × 2, q6h, d2 and d3 6 mg/kg/day po. Under the proposed dosage regimens, the blood concentration of PND could be maintained at a level of about 2 times the blood MEC during 1 min-72 h after first intramuscular injection, and 1 (or 3)-72 h following first oral dosing. However, further clinical studies should be conducted to, evaluate their therapeutic and undesirable effects.