The major urinary metabolites of 1,3-butadiene are monohydroxybutenyl-mercapturic acids (MHBMA) and dihydroxy-butyl-mercapturic acid (DHBMA). These metabolites can be used as biomarkers of exposure to this diene. In order to determine the smoking-related exposure to 1,3-butadiene, we have developed a rapid LC-MS/MS method for the determination of MHBMA and DHBMA in urine of humans and rats. The method requires 2-5 ml of urine which is solid phase extracted prior to LC-MS/MS analysis. Precision for MHBMA is < or =11.2% for human and < or = 17% for rat urine. Corresponding values for DHBMA are < or = 7.2 and < or = 19%, respectively. Recovery rates are approximately 100% for both analytes in human urine and about 115% in rat urine. Limits of detection (LOD) are for humans 0.9 and 23 ng/ml and for rats 1.5 and 33 ng/ml for MHBMA and DHBMA, respectively. Application of the method to urine of humans and rats showed a significant effect of tobacco smoke exposure on the urinary excretion of MHBMA and the metabolic ratio DHBMA/(DHBMA + MHBMA).