To develop a new method for evaluating the intensity of workers. exposures to toluene alone or toluene in mixed solvents, regression equations were calculated between the concentrations of toluene to which workers were exposed and the concentrations of hippuric acid or toluene in workers. urine samples taken at the end of their shifts. Thereafter, the discriminant exposure concentration of the solvents in air, which was the concentration considered to discriminate exposure from non-exposure within a fixed level of error using fiducial ranges of individual specimens (DEC-I) or using confidence ranges of regression equation (DEC-R), was measured by a scale. The devised equations were applied to calculate DEC-I or DEC-R accurately using the formulas expressing a regression line and its fiducial ranges or confidence ranges. The equations can calculate not only more precise values of DEC-I or DEC-R than can be measured by a scale, but can also calculate values corresponding to any level of error. Moreover, DEC-I and DEC-R can be defined by the equations. The concentration capable of discriminating TLV (threshold limit value) exposure from non-TLV exposure was estimated using fiducial ranges (DTL-I) and then using confidence ranges of the regression equation (DTL-R).