The Plasmodium yoelii reticulocyte-binding protein Py235 has a role as an ATP/ADP sensor. The sensor domain of Py235 is called NBD94; it consists of at least three functional regions, the nucleotide-binding region (NBD94(444-547)), hinge region (NBD94(566-663)) and C-terminal coupling region (NBD94(674-781)), and has been proposed to link ATP/ADP binding to the interaction of Py235 with the red blood cell. Here, NBD94(674-781) was cloned, expressed and purified to high purity. The monodisperse protein was crystallized by vapour diffusion. A diffraction data set was collected to 2.9 Å resolution with 97.2% completeness using a synchrotron-radiation source. The crystals belonged to space group C2, with unit-cell parameters a=65.08, b=82.71, c=114.27 Å, β=94.72°, and contained four molecules in the asymmetric unit.