The compatibility and stability of diazepam injection were studied following dilution to 10 different concentrations in dextrose 5% in water, normal saline, Ringer's injection and lactated Ringer's injection. Prepared solutions were examined for clarity and pH throughout a 24-hour period. Clear solutions were filtered and then assayed 24 hours after preparation using UV spectrophotometry. Solutions which formed visible precipitates before 24 hours or which did not demonstrate acceptable potency (greater than or equal to 90%) were assayed after shorter time periods. Dilutions lower than 1:20 (5 mg in 20 ml) resulted in immediate visible precipitates in all four diluents. The 1:20 dilution was compatible with all four diluents and maintained acceptable potency for four hours, whereas at 1:40 dilution (5 mg in 40 ml) diazepam was stable for at least 6-8 hours in the same diluents. At higher dilutions of 1:50, 1:75 and 1:100 (5 mg in 50, 75 and 100 ml, respectively) the injection was compatible with and stable in all four diluents for 24 hours. Further studies are required before the use of diazepam injection as an infusion can be recommended. However, if in some circumstances it is necessary to administer diazepam as an infusion, it is recommended that it be diluted in dextrose 5% in water, normal saline, Ringer's injection or lactated Ringer's injection to a dilution of at least 1:40 and used within 6 hours or to a dilution of 1:50 and used within 24 hours.