T lymphocyte clones specific for malarial (Plasmodium falciparum) blood stage antigens were obtained from acutely infected patients or from donors living in a malaria-endemic area of West Africa. Thirty-four clones carrying the CD4 antigen, and one CD8+ clone, were tested in a proliferation assay for their capacity to recognize P. falciparum isolates of different geographical origins. Only one clone distinguished between different parasite isolates (it failed to react with a parasite isolate originating from East Africa, but did recognize West African and Asian isolates). All of the clones responded well to intact erythrocytes containing viable parasites, but some responded poorly to extracts of parasitized cells. Eight of 19 clones studied (all CD4+) recognized parasite antigens which had characteristic mobilities in sodium dodecyl sulfate-containing polyacrylamide gels. The antigens had apparent molecular weights of about 20,000, 35,000, 40,000, 120,000, 150,000-200,000 and 200,000. These results (together with a previous report of two clones recognizing an antigen of molecular weight about 50,000, Sinigaglia and Pink, EMBO J. 1985. 4:3819) show that T cells in infected individuals react with at least 6 different parasite proteins.