The compatibility of cimetidine hydrochloride and cefoperazone sodium in 5% dextrose injection stored at two temperatures was studied. Cimetidine hydrochloride and cefoperazone sodium were reconstituted or diluted with 5% dextrose injection to form an admixture with a cimetidine concentration of 2 mg/mL and a cefoperazone concentration of 5 mg/mL. The admixture was stored in 100-mL vented i.v. containers in the dark at 4 and 25 degrees C; three containers were stored at each temperature. A 2-mL sample was taken from each container after 0.5, 0.75, 1, 6, 12, 24, and 48 hours of storage and visually inspected, tested for pH, and assayed by a stability-indicating high-performance liquid chromatographic method. Triplicate studies were done for each storage condition. At both temperatures, drug concentrations varied by less than 5% during the study period. No color change, precipitation, or cloudiness was observed for any of the solutions under any of the storage conditions. Cefoperazone sodium 5.0 mg/mL and cimetidine hydrochloride 2.0 mg/mL in admixtures in 5% dextrose injection are stable for 48 hours at 4 and 25 degrees C.