Hippuric acid excretion in the urine of workers after exposure to toluene, was assayed by a modified method of Gaffney's. The results obtained are as follows, 1) The determination of hippuric acid in the urine was carried out by paperchromatography, and 0.1 ml urine was spotted on the filterpaper (40×40cm), developed in the solvent system: buthanol-acetic acid-water, 4:1:1. After drying, the color reaction was brought to completion by spraying with 4 per cent solution of p-dimethylaminobenzaldehyde in acetic anhydride saturated sodium acetate and by heating it in a drying oven for one minute at 135℃. The R(f) value of hippuric acid contained in the urine was 0.8, and it coincided with that of pure hippuric acid, and the absorption spectrum of the methanol eluate of the colored spot of the workers' urine corresponded with that of pure hippuric acid. 2) At the autotricycle factory using the mixture of toluene and benzene (4:1) as a solvent of glue, and also toluene as a component of thinner for spray, an increase of hippuric acid excretion in the urine of workers was recognized after exposure to the solvent gases. 3) In the plastic factory using toluene as a solvent, the group of workers exposed to 50 p.p.m. of toluene in air bad the excretion of the hippuric acid 3.4 times compared with that befor exposure, and the group exposed to 20p.p.m., 1.9 times. These results indicate that the excretion of hippuric acid in the urine is in direct proportion to the concentration of toluene in air.