We report on the preparation, crystallization, and preliminary x-ray diffraction analysis of the Fab fragment of the monoclonal antibody 8F5 that neutralizes infectivity of human rhinovirus serotype 2 (HRV2). Fab fragments prepared from this antibody by papain digestion were purified to isoelectric homogeneity by ion exchange chromatography and chromatofocusing. Crystals were obtained by the hanging drop vapor diffusion method using ammonium sulfate as precipitant. The crystals belong to the orthorhombic space group P2(1)2(1)2(1) with unit cell dimensions a = 59.9 A, b = 86.3 A, c = 128.2 A and diffract to at least 2.8-A resolution. The cell volume suggests the presence of one molecule per asymmetric unit, and the solvent content is estimated to be 61%.