The concentration of nicotine in hair was measured by a capillary gas chromatograph with a nitrogen-phosphorus detector after hair was dissolved in 2.5 N sodium hydroxide and nicotine was extracted using diethyl ether. In hair samples obtained from 36 smokers, who had smoked > or = 3 years, there was a significant positive correlation between the concentration of nicotine and the number of cigarettes consumed daily (r = 0.685; p < 0.001). The nicotine content of white hair was much less than that of black hair collected from the same subjects with grizzled hair. The above findings were confirmed by an animal experiment, in which nicotine (0.2, 0.6, and 2 mg/kg/day for 2 weeks) was administered intraperitoneally to pigmented rats whose hair had been removed beforehand by plucking from an area of the back of each rat. The hair which grew back in the denuded area was plucked and collected one week after the last administration of nicotine. The nicotine concentration in the brown hair of the back correlated with the given dose (r = 0.824; p < 0.001). In a separate experiment, hairs were removed from areas of back and thorax, and nicotine delivered to the rats for 4 weeks by an osmotic pump implanted under the skin, showing that the concentration in the whitish hair was much lower than that in brown hair. Finally, hair samples were collected from 14 subjects who had participated in a smoking cessation program over 6 months and who abstained from cigarette smoking. The axial distribution of nicotine along the hair shafts was determined for each subject.(ABSTRACT TRUNCATED AT 250 WORDS)