Male albino rats of the Donryu strain were divided into 4 groups: the normal control group, tetrachloromethane (CCl4, TCM) group, tetrachloroethylene (CCl2 = CCl2, PCE) group and trichloroethylene (CHCl = CCl2, TCE) group. Each group was consisted of 6 animals. TCM, PCE and TCE were administered orally at a dosage of 13 mmoles/kg as a 50% v/v olive oil solution to rats 24 hours prior to an oral administration of m-xylene (8.2 mmoles/kg as a 50% v/v olive oil solution). The normal control group was administered only olive oil (2.5 ml/kg) 24 hours prior to m-xylene dose. Urine was collected 24, 48, 72 and 96 hours after administration of m-xylene. The urine was analysed for m-methylhippuric acid (m-MHA) by the paper chromatographic method of Ogata et al. The results obtained were as follows: 1) Total urinary excretion of m-MHA in the normal control group was equivalent on a molar basis to about 58% of m-xylene received, and the major portions of the metabolites were excreted on the 1st day. 2) In TCM group, total urinary excretion of m-MHA was about a half of that in the normal control group. It was equivalent on a molar basis to about 30% of m-xylene received (p less than 0.01), and the urinary excretion of m-MHA on the 1st day was significantly less than those of the normal control group (p less than 0.001) and TCE group (p less than 0.05). 3) In PCE group, urinary excretion of m-MHA on the 1st day was significantly less than that of the normal control group (p less than 0.01) and the excretion was delayed. 4) In TCE group, total urinary excretion of m-MHA was slightly but not significantly less than that of the normal control group (p less than 0.05). 5) In TCM-ip group of rats which were given TCM orally 24 hours prior to the administration of m-xylene by intraperitoneal injection, urinary excretion of m-MHA on the 1st day and in 4 days after administration of m-xylene was less than that of the control-ip group.