The stability of ranitidine at low concentration (0.05 mg/mL) in five intravenous infusion solutions (0.9% sodium chloride, 5% dextrose, 10% dextrose, 5% dextrose with 0.45% sodium chloride, and 5% dextrose with lactated Ringer's injections) was studied. Admixtures were stored for seven days at room temperature in 150-mL and 1-L polyvinyl chloride infusion bags. Ranitidine stability in 0.9% sodium chloride injection and in 5% dextrose injection was also examined for up to 28 days, and these data were compared with data obtained at higher ranitidine concentrations (0.5-2.0 mg/mL). At intervals during the storage periods, color, clarity, and solution pH were examined and ranitidine content was determined by a stability-indicating high-performance liquid chromatographic assay. Ranitidine content remained greater than 90% of the initial concentration for more than 48 hours in all infusion fluids except 5% dextrose with lactated Ringer's injection. No visual changes or appreciable changes in pH were observed for any of the solutions. At the dilute concentration, ranitidine was markedly more stable after eight hours in 0.9% sodium chloride injection than in 5% dextrose injection. In 0.9% sodium chloride injection, ranitidine concentrations remained above 95% for up to 28 days, but drug concentrations in 5% dextrose injection fell below 90% after seven days. Stability in 5% dextrose injection improved as ranitidine concentrations increased from 0.05 to 2.0 mg/mL. Ranitidine (0.05 mg/mL) is stable for at least 48 hours at room temperature in all infusion fluids tested except 5% dextrose with lactated Ringer's injection.