The presence of nicotine in sweat obtained from smokers and one non-smoker exposed to tobacco smoke after 4 h to 8 days of nicotine-free time was investigated. Following stimulation of the eccrine glands, sweat samples were taken every hour for 6 h. The total nicotine concentrations, i.e. the sum of nicotine and its metabolites, were determined by radioimmunoassay. The presence of unchanged nicotine was revealed by gas chromatography/mass spectrometry.