The aim of this paper was to study the possible causes for metabolism changes due to ethanol and solvents interactions. In literature the effects of interaction between some solvents (toluene, xilene, TCE, etc.) and ethanol in acute experimental exposure are well known: the ingestion of a moderate amount of ethanol (0.8 gr/Kg) before inhalatory exposure to solvents causes the hematic levels of the solvent itself to increase and the urinary excretion of the main metabolites to decrease. In our study we have analyzed the possible effects of exposure to toluene vapours on elimination of toluene itself in urine, which is a useful biological index of occupational exposure to toluene. 5 healthy volunteers were exposed to toluene vapours (100 mg/m3 for 4 hours) with and without simultaneous ethanol consumption (0.5 g ethanol/Kg body weight) in an exposure chamber. The ethanol was ingested two minutes before entering the chamber and two hours after beginning of exposure in order to reach ethanol and toluene maximal concentrations in blood simultaneously. The blood and urine were collected at the beginning and at the end of exposure in order to measure toluene and ethanol. The analyses were performed by means of a Gas Chromatograph (GC) Hewlett-Packard 5880 A connected with a Mass Selective Detector (MSD). The obtained results show that ethanol causes a decrease in toluene metabolism: in fact, with constant environmental exposure, toluene concentration at the end of exposure increases in blood from 156 micrograms/L to 285 micrograms/L (+84%) in presence of ethanol; the same happens to the amount of toluene eliminated in urine (+45% in presence of ethanol), while the metabolized amount of toluene (hippuric acid in urine) was lower in presence of ethanol (1492 mg/g creatinine in comparison with 2251 mg/g creatinine; 37%). These results show that a moderate amount of ethanol changes toluene metabolism: this phenomenon may be an important source of error in the biological monitoring of solvent exposure.