In recent years, remarkable advances in sensitive analytical techniques have enabled the analysis of drugs in unconventional samples, such as sweat. In a study conducted with cigarettes smokers and nonsmokers, PharmChek sweat patches were applied to 29 subjects for 72 h. Nicotine was extracted in 5 ml methanol in the presence of 200 ng nicotine-d4, used as internal standard. After 20 min agitation, the methanolic solution was evaporated to dryness in the presence of 10 microl octanol to ensure nonvolatility of nicotine. Nicotine was determined using gas chromatography coupled to mass spectrometry after separation on a 30-m capillary HP5 MS column. The assay was linear in the range 50-2500 ng/patch, with an extraction recovery of 76+/-5%. Limit of detection was 10 ng/patch. Nicotine concentrations in sweat were not detected for the nonexposed nonsmokers (n = 8), 87 to 266 ng/patch for the passive smokers (n = 6) and 150 to 2498 ng/patch for the smokers (n = 15). This study demonstrated a useful application of the sweat patch for monitoring tobacco exposure.