Abstract: The asexual stages of P.berghei ANKA were completely eliminated as revealed in a "4-day suppressive test" with the daily dose of pyronaridine 12.5mg base/kg or amodiaquine 25 mg base/kg.Mefloquine 25 mg base/kg and qinghaosu 100mg/kg though exerted obvious suppressive effect,the cure rates were only 50% and 0%,respectively.In treating chloroquine-sensitive P.berghei ANKA strain pyronaridine exhibited the best therapeutic activity,which was followed by amodiaquine,mefloquine and qinghaosu.In treating moderately chloroquine-resistant P.berghei NS line the cure rate of pyronaridine 12.5mg/ kg·d×4 was 70% ,but none of the 10 infected mice from any group was cured by amodiaquine 100 mg/kg2d,mefloquine 100 mg/kg·d or qinghaosu 200 mg/kg·d.Though the latter 3 drugs showed prominent suppressive effects,parasitemia remained positive or recrudesced after dosing.We demonstrate that parasites resistant to chloroquine had cross resistance to amodiaquine,mefloquine and qinghaosu at various degrees.Amodiaquine 100 mg/kg·d,mefloquine 100mg/kg·d and qinghaosu 200 mg/kg·d exhibited no obvious suppressive activity on highly pyronaridine-resistant line of P.berghei,indicating the existence of cross resistance to pyronaridine.