Healthy volunteers aged between 15-45 years were screened at two centres for their eligibility to take part in the study. Screening involved a thorough physical examination as well as blood sampling tests for haematological (full blood count, packed cell volume [PCV]), renal (plasma creatinine level) and hepatic (alanine amino transferase) tests and for HIV 1 and 2 tests by ELISA. A glucose-6-phosphate dehydrogenase (G6PD) deficiency test was carried out because of the risk involved with administering the study drugs Primaquine and Lapdap to volunteers who are G6PD deficient. Exclusion criteria included a PCV < 30%, raised plasma creatinine (> 130 micromoles/litre) or ALT levels (> 42 IU/litre), G6PD deficiency, simultaneous participation in another clinical trial, blood transfusion in the month prior to vaccination, previous experimental malaria vaccination, administration of another vaccine within 2 weeks of vaccination, allergy to any previous vaccination or to sulphadoxine/pyrimethamine, history of splenectomy and any treatment with immunosuppressive drugs.