Antibodies to Pf155, a major Plasmodium falciparum antigen detected in the membrane of glutaraldehyde-fixed and air-dried erythrocytes infected with P. falciparum, were studied in serum samples collected from patients treated for neurosyphilis by induced P. falciparum infection. In 3 patients with no previous documented exposure to malaria, the antibodies were detected late and reached low titers. In 5 patients with extensive previous malaria infections, the antibodies appeared rapidly and reached high titers. The immunofluorescence findings were confirmed by immunoblots. No correlation was observed between antibodies to Pf155 and antibodies detected by standard immunofluorescence with whole parasite antigen.