The effect of inhalation of coal fly ash for 6 hr daily for 15 days has been studied on the hematology, blood chemistry, and histopathology of lungs and liver of rats up to 4 months from the first day of exposure. Fly ash inhalation significantly reduced WBC, RBC, and hemoglobin contents at earlier periods after exposure but tended to return to normal values at later periods. Fly ash inhalation reduced lymphocytes and increased polymorphonuclears up to 60 days after exposure and after that the alterations were reversible. Blood glucose increased and blood urea and acid phosphatase decreased at early periods after inhalation, but at later periods returned to control group values. Fly ash inhalation profoundly affected the histological structure of lungs and liver at early periods after inhalation. Numerous fly ash-laden macrophages, thickening of alveolar septa, and alveolar dilatation were noted. In the liver, periportal necrosis was also observed. These changes, however, were reversible.