Over the past few years, considerable progress has been achieved in the molecular characterization of some of the constituent proteins of Plasmodium vivax (Pv) merozoites. These proteins include the P. vivax membrane surface protein (MSP) PvMSP-1 and three other MSP that have been designated PvMSP-2, PvMSP-3 and PvMSP-4. Additionally, three other merozoite proteins involved in the receptor-mediated adhesive interactions that occur during invasion have been molecularly defined. One of these merozoite adhesins, the Duffy-binding or -adhesion protein, interacts with Duffy glycoprotein, whereas the other two, reticulocyte-binding proteins serve to target reticulocytes. A fourth merozoite protein that has been identified, the merozoite apical cone protein, is also likely to be involved in adhesion and invasion.