A rapid and simple high-performance liquid chromatographic analysis of nitrazepam in plasma with temazepam as an internal standard is described here. Alternatively, this assay method can also be used to determine temazepam plasma concentrations with nitrazepam as the internal standard. Chloroform was used as an organic solvent for the extraction process. The percentage recoveries of nitrazepam and temazepam were 79% and 85%, respectively. The coefficient of variation of the within-day precision of the assay procedure at a concentration equal to 50 ng/ml of nitrazepam was 2.4% (n = 5), and that for day-to-day precision at the same concentration was 4.7% (n = 5). Calibration curves for nitrazepam and temazepam were linear over their therapeutic ranges. Pharmacokinetic parameters obtained with this method after a single oral dose of 5 mg of nitrazepam in five normal subjects were comparable to results obtained in previous studies.