To investigate the osmolality of commercially supplied drugs used in anesthesia, the authors measured the osmolality of a total of 62 drugs with osmometer using the principle of freezing point depression. The osmolality range of drugs observed was 0-12,478 mOsm/kg water. The drugs of osmolality between 240 and 340 mOsm/kg water were 21(34%). Hypertonic drugs(<240 mOsm/kg water) were 18(29%) indicating two-thirds of the drugs were hypo-or hypertonic. Therefore, it is recommended that extreme hypo-or hypertonic drugs should be administered cautiously especially when they are administered rapidly and massively in order to prevent hemolysis or cell shrinkage.