The effect of carbon tetrachloride on the excretion of HA and m-MHA, metabolites of toluene and m-xylene, respectively, was examined. Urine was collected before the injection and 24, 48 and 72 hours after the injection and analysed for HA or m-MHA by HPLC. Total excretion of HA in the urine of rats injected with toluene and carbon tetrachloride (subcutaneously) was less than when toluene alone was injected. The more carbon tetrachloride was injected the less was the total excretion of HA in the urine. Total excretion of m-MHA in the urine of rats injected with m-xylene and carbon tetrachloride (subcutaneously) was less than when m-xylene alone was injected.