Cotinine levels in blood, urine and cervical fluid of smokers and nonsmokers were analyzed by capillary-column gas chromatography. The sensitivity of this method appeared to be 100%. The specificity was lower (87.5% in blood, 25% in urine and 75% in cervical fluid). Nonsmokers exposed to smoke by others had low but detectable cotinine levels in the three body fluids. The highest cotinine levels in cervical fluid were detected during the proliferative phase of the cycle. Cotinine levels in cervical fluid and blood correlated well, but the correlation was less during the proliferation phase. Cotinine measurement in cervical fluid proves to be a reliable method to quantify exposure to tobacco smoke, even when induced by others.