Hair from 80 male subjects, smokers and non-smokers, was exposed continuously in a dynamic exposure chamber to constant nicotine vapour concentrations of 20, 200 or 2000 micrograms/m3 for 72 hr. Subgroups of high and low nicotine adsorbing hair were also exposed intermittantly to environmental tobacco smoke for 8 months. Air and hair concentrations of nicotine were determined by gas chromatography/mass spectrometry. The chamber experiments demonstrated a hair nicotine uptake which followed a second order relation to the applied concentrations of nicotine, y = -0.00018x2 + 0.715x + 1.13, r2 = 0.99999. The function and the experimental points showed linearity up to an air nicotine vapour concentration of about 200 micrograms/m+, covering the most relevant range of environmental exposure. An approximately 7- and 2-fold interindividual variation was observed in the hair uptake rate constant of nicotine vapour for the investigated material within the 10 to 90 and 25 to 75% percentiles, respectively. The factors causing this variation were not identified. It was shown that subject age, hair diameter and hair content of eumelanin were without correlation to the rate constants of hair nicotine uptake. The exposure of subgroups of hair to environmental tobacco smoke showed similar uptake profiles of nicotine as that experienced with exposure to pure nicotine vapour, supporting the relevance of controlled chamber nicotine vapour exposures as a relevant tool for the evaluation of hair nicotine uptake from a more complex environmental situation. Standardized measurements of air nicotine vapour and particulate concentrations in a modern office during 3 hr periodical smoking periods, showed that the number of cigarettes smoked was a poor indicator for the estimation of individual exposure to environmental tobacco smoke constituents. Hair nicotine measurements so far seem to be superior to other suggested methodologies for estimation of environmental tobacco smoke exposure, but further studies should be initiated to identify factors determining the rate constant of hair nicotine uptake.