A method for biological monitoring of urinary 2-(thiocyanomethylthio)benzothiazole (TCMTB), a wood preservative and an industrial chemical, was developed. Three different doses of TCMTB in olive oil were given to male rats by gavage for 3 weeks. Urine was collected daily and the metabolites were analysed as thioethers by derivatization with pentafluorobenzyl-bromide by gas chromatography-mass spectrometry. The parent chemical was not detected in urine samples, but two metabolites of TCMTB were identified. 2-Mercaptobenzothiazole (2-MBT) was the main metabolite, and its excretion varied according to the dose. The second metabolite was 2-(mercaptomethylthio)benzothiazole. The amount of 2-MBT excreted in rat urine was 66 +/- 12% (SD), 51 +/- 20% and 44 +/- 9% for TCMTB doses of 15, 75 and 150 mg/kg, respectively. Two doses, 75 and 150 mg/kg, caused diuresis in rats during the 1 week of dosing. During the 3-week TCMTB treatment, rat liver microsomal CYP enzyme profile was not significantly changed. Urine samples of sawmill workers exposed to TCMTB were collected after their work shifts for exposure assessment. TCMTB could not be detected in the urine samples of exposed workers. Most concentrations of 2-MBT were below the limit of the detection, 0.12 mumol/l, the concentrations were 0.12-0.15 mumol/l only in few cases. The determination of 2-MBT in urine, when a sample is taken immediately after a work shift, is a suitable indicator of workers' exposure to TCMTB.