Many reports have been made on the hematological study of workers exposed to tri- and perchloroethylene vapors, but they covered small number of persons and only erythrocyte and leucocyte numbers and sometimes hemoglobin values were measured. The authors examined erythrocyte counts, leucocyte counts, hemoglobin values, hematocrit readings, specific gravity of blood and differential counts of leucocytes on 162 workers (male 136, female 26) exposed to above mentioned vapors, and found no remarkable abnormality in every item of examinations. This finding is in agreement with the results of almost all researches so far as the authors know, with but one exception.