AbstractFreezing tissue for intraoperative diagnosis often introduces artifacts that make subsequent histologic evaluation of routinely processed tissue difficult. While attention has been given to methods of improving the quality of the frozen section itself (microwave irradiation and pretreatment with dimethyl sulfoxide), little attention has been given to the production of optimal microscopic image quality in the permanently processed“frozen section control.”One hundred sections of liver from a single human autopsy were each frozen in a cryostat in OCT compound at−20°C; the sections were then transferred to one of five postfrozen section solutions-formalin, Omnifix, Tris buffer (.05 M, pH 7.6), B5, and ethylene glycol. Routine hematoxylin and eosin sections were prepared. Each of the 100 sections was graded blindly with assessment of four features: preservation of chromatin detail, preservation of nucleoli, preservation of cytoplasmic detail, and maintenance of cell borders. The superior postfrozen medium proved to be 10% formalin, which provided a greater preservation of nuclear and cytoplasmic detail than did the other four media. (The J Histotechnol13:289, 1990)