 Phase IIIa double-blind randomized adjuvant-controlled trial. 16 volunteers are randomized to receive two doses of either 30 μg of PfCS102 formulated in Montanide ISA 720 verum or ISA 720 alone control, 60 days apart. Two weeks after the 2nd immunization, 14 volunteers are challenged with bites of 5 infected mosquitoes using the NF54 strain of P. falciparum. The main outcome will be the length of time between artificial challenge and development of blood stage parasitaemia detected by microscopy performed twice a day. 