Study to monitor the susceptibility of P. falciparum to chloroquine in south Iran was conducted in Bandar Abbas. Forty-five falciparum malaria subjects who had received 25mg. chloroquine base per kg. body weight over 3 days were followed up for 4 weeks, while three other patients for a period of 1-3 weeks. No recrudescence could be confirmed among the subjects during the follow up of the study. The mean time of asexual parasites clearance was 2.15 days. The action of chloroquine against the asexual form of P. falciparum in the present study was suspected to be slower as compared with those observed in the previous studies. However, both in vivo and limited study using the in vitro technique showed that the response of P. falciparum asexual parasites to chloroquine was still satisfactory. The study supports previous findings in Ethiopia that acquired immunity malaria had no significant effect on the asexual parasite clearance time.