The pore structure of column-packing materials plays a significant role in high-performance liquid chromatography (HPLC) and will be particularly important for the separation of macromolecules. In this study, spherical, porous zirconia particles 5-10 mu m in diameter were synthesized by the controlled aggregation of 700-Angstrom colloids, Two different aggregation methods were used : oil emulsion processing and polymerization-induced colloid aggregation (PICA), The pore structures of the resulting materials were characterized by electron microscopy, nitrogen adsorption/desorption, mercury (Hg) intrusion/extrusion, pulsed field gradient spin-echo NMR self-diffusion measurements, and NMR spin-lattice relaxation measurements. The tortuosity and hydraulic diameter resulting from the two aggregation methods are compared, The PICA-generated sample is less porous but shows a more well-connected pore structure, These results show the need to restore high porosity while retaining the beneficial pore structure and the high degree of control of aggregate size that are characteristics of the PICA process.