Using the Panama II strain of Plasmodium falciparum obtained from continuous in vitro culture as antigen, the micro enzyme-linked immunosorbent assay (ELISA) was used to test serum samples from 50 persons from the southeastern United States and serum specimens collected weekly from four non-immune and nine semi-immune patients infected with P. falciparum. None of the 50 sera from the United States had ELISA antibody titers ⩾1:80. The nine semi-immune patients had rapid ELISA antibody responses (titers ⩾ 1:2560) following patent parasitemia. ELISA titers remained elevated despite disappearance of patent parasitemia, and declined gradually following curative antimalarial therapy. The ELISA responses observed in the four non-immune patients were more variable, though positive titers appeared rapidlly with patent parasitemia. Maximum titers were lower than those observed in semi-immune patients. These results demonstrate that P. falciparum obtained from continuous in vitro culture is an excellent antigen for the micro-ELISA test for malaria. However, further assessments of the ELISA are needed to identify the conditions associated with positive responses.