The responses of Plasmodium falciparum to antimalarial drugs were evaluated through the in vitro test using blood sample collected from patients of 7 municipalities of the south of Pará State. Sixty nine microtests for chloroquine and mefloquine, 62 for amodiaquine and 61 for quinine were performed. The results showed a high resistance for chloroquine (71%), a relatively low resistance level for amodiaquine (25.8%) and little resistance to quinine (8.2%). For mefloquine 100% of sensitivity was found.