A 12 ammo-acid synthetic peptide (NANP)3 comprising the immunodominant epitope of Plasmodium falciparum circum-sporozoite protein was conjugated to tetanus toxoid (TT), adjuvan-ted with aluminium hydroxide, and administered intramuscularly in three doses at monthly intervals to 35 healthy males as a malaria vaccine. No significant adverse reactions were noted, with mild soreness at the injection site the only common symptom. Serocon-versions against NANP occurred in 53% and 71% of recipients of 100 or 160 μg, respectively, measured by enzyme-linked immunosorbent assay (ELIS A). Most ELISA-positive sera reacted with sporozoites by indirect immunofluorescence (IFA). Three vaccinees with the highest ELISA and IFA titres and four unim-munized controls were challenged with P. falciparum sporozoites introduced via the bites of infective Anopheles mosquitoes. Blood stage parasites were detected in all controls by 10 days (mean 8.5 days, range 7–10). In contrast, the two vaccinees who became infected did not manifest parasitaemia until day 11 and the third vaccinee showed neither parasites nor symptoms during the 29 day observation period. This first synthetic peptide parenteral vaccine against a communicable disease tested in man is safe and stimulates biologically active antibodies. These observations encourage the development of improved vaccine formulations which, by enhancing immunogenicity, may lead to practical vaccines to assist in the control of falciparum malaria.