 Volunteers will be given up to six vaccinations over three months and will then be exposed to malaria infection. We do this by allowing mosquitoes infected with malaria to bite them under closely regulated conditions and observing if and when they develop blood stage malaria. If the vaccines provide some protection from malaria infection then either they will not develop malaria after the bites or the time taken to develop malaria will be longer. If not all volunteers are protected then we will be able to try and improve our vaccines by comparing the immune responses of volunteers who are protected to those not protected. 