The purpose of this study is to evaluate the hematological changes of workers exposed to mixed organic solvents and to search the organic solvent that bring out these changes. The study participants were 1,605 workers, consisting 1,088 workers (male 989, female 99) exposed to mixed organic solvents and 517 non-exposed workers (male 431, female 86). The authors analyzed the results of complete blood count and differential count of leukocytes of all the workers and examined all of the material safety data sheets of substances with which they dealt and the results of their working environmental surveys during the last 3 years. The results were as follows: 1. The mean values of complete blood count in workers exposed to mixed organic solvents were lower than that of non-exposed workers in WBC, RBC, hemoglobin and hematocrit in cases of male and RBC, hemoglobin and hematocrit in cases of female, but the mean value of platelet count in male exposed workers and WBC count in female exposed workers were higher than those of non-exposed workers. 2. The distribution of differential count of leukocytes showed no difference between exposed workers and non-exposed workers. 3. The correlation coefficients between age and duration of employment and WBC showed statistically a positive value and that between age and duration of employment and RBC, hemoglobin, hematocrit showed a statistically negative value in cases of male exposed to mixed organic solvents. But in cases of female there was no statistical correlation between them. 4. In cases of male the proportions of workers with subnormal levels of WBC, RBC, hemoglobin, hematocrit and platelet according to the standard of classification were high or than those of non-exposed workers. The proportions of exposed workers were 3.6 %, 18.6 %, 5.3 %, 32.7 % and 1.4 % respectively and those of non-exposes workers were 2.8 %, 10.7 %, 2.1 %, 13.9 % and 0.2 % respectively. 5. In cased of female the proportion of workers with subnormal levels of RBC, hemoglobin and hematocrit according to the standard of classification were higher than those of non exposed workers. The proportion of exposed workers were 42.4 %, 55.6 % and 41.4 % respectively and those of non-exposed workers were 10.5 %, 11.6 % and 8.1 % respectively. 6. The number of substances with which workers exposed to mixed organic solvents dealt were about 500, and 22 organic solvents such as xylene, toluene, isopropyl alcohol, 2-ethoxyethanol and 2-ethoxy ethyl acetate were main components of substances according to the material safety data sheet and working environmental surveys during the last 3 years. The authors suspect 2-ethoxyethanol and 2-ethoxy ethyl acetate of the organic solvents, which bring out the hematological changes of workers exposed to mixed organic solvents. As a result of this study, the authors confirmed the hematological changes of workers exposed to mixed organic solvents and recommend : strict management of working environment, working time and the protective equipments of workers exposed to mixed organic solvents.