More than 120 years after Alphonse Laveran's discovery of the blood-stage malaria parasite, there is no licensed malaria vaccine and malaria remains the world's most serious parasitic disease. Efforts to develop a vaccine have been thwarted by the complexity of the parasite's life cycle and the ability of the parasite to suppress and evade the immune response. Currently, there are several candidate vaccines in clinical trials and many more candidate vaccines that have shown efficacy in animal models or are based on studies of the immune responses of people who are resistant to malaria. The sequencing of the genomes of Plasmodium falciparum and Plasmodium yoelii yoelii in 2002 is expected to result in the identification of previously-unknown candidate vaccine targets from various stages of the Plasmodium life cycle. A great deal of effort is going into identifying the correlates of protection, potentially allowing more efficient testing of candidate vaccines in the future. The fact that a vaccine candidate has shown partial protection in field trials is a reason for hope that, with the proper effort and support, effective vaccines against malaria can be developed.