High-performance liquid chromatography was used for measuring the air nicotine content and determining the air nicotine content and determining simultaneously nicotine and its main metabolites, free and conjugated, in urine of non-smokers diversely exposed to environmental tobacco smoke (ETS). Three studies were realized on periods of 24 hours, among adults occasionnally or chronically exposed and among children exposed to parental smoking. Air quantities of nicotine inhaled from air were between 5 and 292 µg for 24 hours. If the whole nicotine was inhaled and absorbed by the non-smoker, the "cigarette-equivalent" (producing 1 mg nicotine each for the active smoker) could be estimated for 24 hours from 0.005 to 0.29 (mean 0.10, close by the value of 0.11 obtained in a previous study). Urine concentrations of nicotine and its metabolites determined in view of establishing a possible relationship between the inhaled alkaloid and "the nicotine-equivalents" excreted during a same period of 24 hours, were very low or only represented 9 to 91 % (mean 47 %) of the air nicotine content i.e . 0.01 to 0.17 (mean 0.05) "biological cigarette-equivalent". In all cases the impregnation by ETS on a whole day was low. Inter-individual and even intra-individual differences were observed. The adults chronically exposed were the most affected by ETS; weakly were the other ones exposed and lesser the children of smokers. The biotransformation of nicotine seemed to be especially important when the exposition to ETS was often repeated