Amodiaquine cured 38% (13/34) of patients with falciparum malaria in Southeast Thailand. Chloroquine cured 0% (0/13). The cure rates with amodiaquine were the same whether a 1.5 g or 2.0 g course was used. Most patients were resistant to amodiaquine at the RI level and to chloroquine at the RII level. In hospital, amodiaquine cleared parasitemia more frequently than did chloroquine. With the 2.0 g course of amodiaquine, the parasite clearance time was 77 hours; the fever clearance time of 36 hours was low and suggests that amodiaquine does not cause a drug fever. Because of resistance, chloroquine should not be used for falciparum malaria in Thailand. Routine use of amodiaquine is not indicated because more effective drugs are available.