Abstract: 　AIM:To observe the variation in resistance of Plasmodium falciparum after the cessation of chloroquine medication. METHODS:WHO standard in vitro microtest and in vivo test were used. RESULTS: In vitro test showed that the rate of chloroquine resistant P.falciparum dropped from 97.9% in 1981 to 26.7% in 1997 ( P<0.001). The mean concentration of chloroquine for complete inhibition of schizont formation declined from 10.46±7.14 pmol/ul blood in 1981 to 1.63±1.47 pmol/μl blood in 1997( P<0.001). In vivo test showed that the rate of chloroquine resistant P.falciparum decreased from 84.2% in 1981 to 18.4% in 1997 (P<0.001) . The proportion of RⅢ cases to the total resistant cases dropped from 53.1% in 1981 to 14.3% in 1997. CONCLUSION:A tendency of progressive decline of resistance of the parasite was revealed after the cessation of chloroquine medication.

Key words: Plasmodium falciparum, resistance, sensitivity, chloroquine.