Thirteen subjects participated in a clinical study to determine the cumulative excretion, the time course, the dose-concentration relationship, and concentrations of diazepam in sweat following oral administration of single dose of the drug. Nordiazepam and oxazepam, two metabolites of diazepam, were also investigated. Sweat was collected by means of Sudormed sweat patch. Patches were removed at specified times over one week and drug content was determined by gas chromatography/mass spectrometry (GC/MS) in negative chemical ionization mode using deuterated internal standards. Irrespective of the time of collection, diazepam and nordiazepam were present, but oxazepam was never detected. Drugs were detectable in the 2 to 4-h period following the administration. Peaks of diazepam were obtained during the 48 to 72-h period. After the peak, a decrease of drug concentration was observed. Concentrations were in the range from 0.1 to 6.0 ng/patch for both drugs. After single administration of diazepam (10, 20, or 30 mg), drugs monitored in three groups of three subjects were suggestive to be dose related. All these data suggest that the sweat patch technology can be useful to document drug use over a week-long period of surveillance.