Six imported cases of chloroquine-resistant Falciparum malaria have been studied since October 1984. In five cases including two Iranian men, returned from India, two Afghan and one Bengalee immigrants came to Iran through Pakistan, recrudescence occurred following treatment with chloroquine. In these five cases resistance of P. falciparum to chloroquine was clinically (by the in vivo test) at R1 level in all patients. The resistance was also confirmed by the macro in vitro susceptibility test which was carried out in four of them. These five chloroquine-resistant cases were treated, one with Sulfadiazine-Pyrimethamine, three with Quinine-Sulfadiazine-Pyrimethamine and one with Sulfadoxine-Pyrimethamine (Fansidar) successfully. In the sixth case who was a Pakistani tourist the parasites showed resistance in the macro in vitro test, but apparently responded to chloroquine treatment in three days. It seems the resistance in this case was also at R1 level as other cases.