Among the surface-exposed antigens of the malaria parasite, those with known essential functions that can be disrupted by antibodies represent the most promising candidates for development as malaria vaccines. Two recombinant protein subunits of the Plasmodium vivax merozoite surface protein 1 have been shown to bind to reticulocytes in enzyme-linked immunosorbent assays. This article discusses the importance of such pre-clinical analyses in the validation of candidate vaccine molecules for P. vivax, given the constraints imposed by the use of primate models and the cost of producing suitable material for human trials.