This article deals with the preparation and morphological characterization of porous materials obtained by freezing and lyophilizing silk fibroin solutions. When an aqueous silk solution is frozen at different temperatures (-18, -45, and -80-degrees-C), the average pore size decreases with lowering of the freezing temperature. Silk fibroin aggregates obtained in these conditions exhibit a sheetlike structure. By lowering the pH from neutrality to 4.01 and 2.65, the morphology of the solid phase changes from a sheet to a fiber structure. The average pore size is smaller at pH 4.01 than is the former value corresponding to the isoelectric point of silk fibroin. The addition of different amounts of methanol to the silk solution results in a sharp fall of the average pore size and hardens the material, as a consequence of the high packing density of the fibroin molecules. Silk fibroin aggregates prepared in these conditions exhibit a typical fibrous structure. A drug-delivery system was prepared by incorporating acetylsalicyclic acid into a porous silk fibroin carrier, and the kinetics of the drug release was studied.