The applicability of a recently developed octadecylalumina (ODA) stationary phase for the preparative separations of proteins and peptides is compared with that of conventional Octadecylsilica (ODS) phases. Chromatographic peak widths, peaks areas, and recoveries of polypeptides were obtained from both types of phases. The ODA phase compares favorably with the ODS phase on small peptides, but exhibits low recoveries on high molecular weight proteins. The results are attributed to the unique fused-microplatelet shape of the ODA particles.