We analyzed the urine of nonsmoking hospital workers exposed to environmental tobacco smoke for [4-(methylnitrosamino)-1-(3-pyridyl)but-1-yl]-beta-O-D-glucosiduronic acid (NNAL-Gluc), a metabolite of the tobacco-specific lung carcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone. Samples were collected three times on a single day from nine workers. Quantitative analysis was carried out by combined gas chromatography-nitrosamine-selective detection. The identity of NNAL-Gluc was confirmed by combined gas chromatography-tandem mass spectrometry. The results demonstrated the presence of NNAL-Gluc in the urine of the exposed subjects. The mean level of NNAL-Gluc +/- SD was 0.059 +/- 0.028 pmol/ml urine (23 pg/ml urine); range, 0.005-0.11 pmol/ml urine. Levels of NNAL-Gluc per milliliter of urine correlated with those of cotinine (r = 0.51; P = 0.029). These results demonstrate for the first time that NNAL-Gluc, a metabolite of the lung carcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone, is present in the urine of nonsmokers exposed to environmental tobacco smoke under field conditions.