H2-proteinase, a non-hemorrhagic metalloproteinase from the venom of Trimeresurus flavoviridis, has been crystallized by vapor diffusion from solutions containing ammonium sulfate. The crystals belong to the tetragonal space group, P41212 or P43212, with unit cell dimensions of a = b = 77.8 A and c = 82.3 A. The asymmetric unit contains one protein molecule. Diffraction data for a native crystal were collected up to 2.0 A resolution.