To validate data on tobacco use, the authors investigated the use of hair samples for quantifying nicotine and cotinine by gas chromatography/mass spectrometry. Hair was taken from 22 nonsmokers and 42 smokers, cut close to the scalp at the back of the head. The hair (about 100 mg from each subject) was incubated in 3 mL of 1N NaOH at 100 degrees C for 1 h. After this, the samples were extracted by diethyl ether. The drugs were separated on a 12-m BP-5 capillary column and detected using selected ion monitoring (nicotine, m/z 84; cotinine, m/z 98). Hair from nonsmokers and smokers contains nicotine and cotinine. Although it is difficult to determine an absolute cutoff level, an amount greater than 2 ng of nicotine per milligram of hair can be used to differentiate smokers from nonsmokers. In the population of nonsmokers, the influence of environmental smoke exposure was noted.