A reliable and sensitive method for the simultaneous determination of nicotine and cotinine concentrations in various human tissues was developed using capillary gas chromatography/mass spectrometry. Nicotine and cotinine were extracted using a 3-step solvent extraction procedure and quinoline as an internal standard. Quantification was carried out by single ion monitoring using ions of m/z 133 for nicotine, m/z 176 for cotinine and m/z 129 for quinoline. The lower limit of detection was 5 ng/g for nicotine and 10 ng/g for cotinine, in each tissue sample. The calibration curves of various tissues were linear in the concentration range from 5-1,200 ng/g for nicotine and 10-1,500 ng/g for cotinine. The accuracy and precision of this method were examined using human tissues and the results were satisfactory. The distribution of nicotine and cotinine was measured in tissues from 10 human autopsies. Nicotine was detected in every tissue examined at a level seen in habitual smokers. The nicotine concentration was high in the liver, kidney, spleen and lung, and low in adipose tissue. The cotinine level was highest in the liver. The tissue/blood concentration ratios of nicotine and cotinine were most stable in skeletal muscle, where the level of these drugs was close to that in whole blood. Skeletal muscle is, therefore, considered to be the most suitable tissue sample for toxicological examination, when acquisition of blood samples is not feasible.