Relation between air concentration of organic solvents in the factory using thinner and urinary glycine conjugates of volunteers exposed to thinner was examined. The results were obtained as follows. Three volunteers were exposed to thinner containing major m-xylene for one hour in the room where ceiling was opened. One volunteer out of three ones used the gas mask, but the others did not use it. The urinary glycine conjugates at time lapsis measured of the volunteers urine. Air density which averaged hourly air solvents concentration in the shop was mainly coinceid with air density which calculated from urine that excreated from two volunteers without gas mask, using the chart deveiced by Ogata et al.(1)) The urinary glycine conjugates of volunteer with gas mask was not so exchange after exposure. From these results, Ogata's report made by steady account of m-xylene applied to the shop where air density change and gas mask was high efficiency of trapping to work in the high concentration of organic solvents, in this instance.