Apical membrane antigen 1 (AMA1), a type 1 transmembrane protein present in the microneme organelles of Plasmodium, is a leading malaria-vaccine candidate. The ectoplasmic region of AMA1 from P. vivax has been expressed in Pichia pastoris and crystallized in two different forms: an orthorhombic form (space group P2(1)2(1)2(1), unit-cell parameters a = 54.1, b = 76.1, c = 103.9 A) and a monoclinic form (space group C2, unit-cell parameters a = 150.0, b = 53.8, c = 60.3 A, beta = 113.2 degrees ). Native data have been collected to 2.0 A resolution for the orthorhombic form and 1.8 A for the monoclinic form. A platinum derivative was prepared for the orthorhombic and monoclinic crystals using K(2)PtCl(4) and data were collected at several wavelengths to obtain phases by the MAD technique. A partial model has been built from the electron-density maps of both forms and refinement is in progress.