A reverse-phase HPLC system using a microparticulate hexyl bonded-phase column and a methanol-water mobile phase was employed to quantitate diazepam in its injectable formulation. The method was accurate over the range of 15 to 150 ng on column, as employed in our laboratory, corresponding to 0.6 - 6 mg/ml of diazepam in the injection solution. It was precise (3.97 to 4.63% coefficient of variation) and has been used in stability studies of diazepam. The method was also used to quantitate a degradation product of diazepam, 2-methylamino-5-chlorobenzophenone, over the range of 0.5 to 4.5 ng on column (corresponding to 20-180 ug/ml in the injection solution) with a precision of 2.18 to 7.07% coefficient of variation. Samples were prepared by dilution with methanol containing biphenyl as internal standard. Each chromatogram required about 6 minutes.