Cotinine is a major metabolite of nicotine. This study was planned to investigate the relationship between bronchoalveolar lavage (BAL) fluid cotinine levels and serum cotinine levels in smokers and nonsmokers with various pulmonary diseases and to investigate whether these levels are affected by passive smoking. Serum and BAL fluid cotinine levels were measured in 27 patients. BAL cotinine levels were measured using a sensitive ELISA kit produced to measure cotinine in saliva. Plates were read by microuant (BioTek, USA) micro plate reader. All patient serum cotinine levels were detectable except for one nonsmoker patient. However, BAL fluid cotinine levels were measurable in only 6 patients (two of them were nonsmokers). A significant positive correlation was seen between serum and BAL fluid cotinine levels (r = 0.726; p = 0.000). Serum cotinine levels were significantly higher in present smokers than non-smokers (21.0 +/- 16.01; 5.35 +/- 7.65; p = 0.004). However, there were no significant differences in BAL fluid cotinine levels between smokers and nonsmokers. Passive smoking can increase nicotine metabolites in serum and other body fluids, including BAL fluid. Since BAL fluid and serum cotinine levels were well correlated, there is no need to use invasive procedures, such as bronchoscopy and expensive, time consuming BAL fluid analyses. Serum cotinine levels can give a rough idea of smoking status. BAL fluid cotinine meaurements should be done for only scientific reasons.