The chemical stability of cefonicid sodium in infusion fluids was analyzed. Cefonicid sodium vials were reconstituted and diluted with sterile water for injection and other commonly used intravenous fluids to concentrations of 325, 220, 40, 20, and 5 mg/mL. Cefonicid concentration was analyzed by high-performance liquid chromatography initially and after storage at room temperature and 5 degrees C. Reconstituted vials were frozen as long as eight weeks, thawed, and kept at room temperature and 5 degrees C and then analyzed. Cefonicid sodium reconstituted in each of the diluents studied exhibited no change in clarity and very little change in potency after 24 hours at room temperature and after 72 hours at 5 degrees C. Some vials with high concentrations became turbid between 72 and 96 hours at 5 degrees C. The thawed vials were chemically stable for 24 hours at room temperature and for 96 hours at 5 degrees C. When reconstituted with sterile water for injection and other commonly used intravenous fluids, cefonicid sodium vials and small-volume infusions are chemically stable for 24 hours at room temperature and for 72 hours at 5 degrees C. Reconstituted cefonicid sodium vials can be frozen and stored for as long as eight weeks, thawed, and then kept at room temperature for 24 hours or at 5 degrees C for 72 hours.