A gas chromatography-mass spectrometry method was developed for the analysis of flunitrazepam (FN) and its major metabolite, 7-amino-flunitrazepam (7-amino-FN), in both plasma and whole blood. The method was based on acid hydrolysis of the samples after dilution with HPLC water followed by extraction and derivatization (heptafluorobutyrate) of the resulting benzophenones. Analysis of plasma and whole blood samples from subjects administered 2-mg doses of FN showed that FN was only detected in whole blood (LOD 5 ng/mL) and not in plasma. However, 7-amino-FN was detected in both plasma and whole blood, although the levels were much higher in plasma. 7-Amino-FN was detected for the entire period of specimen collection (12 h), but FN was only detected in whole blood for 4 h after ingestion with peak levels after 1 h.