Sprague-Dawley rats and AKR/J mice were exposed to 300 ppm benzene vapor for 6 h/d, 5 d/wk, for life. Rats exhibited lymphocytopenia, mild anemia, and moderately decreased survival. Mice showed severe lymphocytopenia and anemia accompanied by granulocytosis and reticulocytosis. Treated mice also showed significantly decreased survival and weight gain. No indications of a leukemic or preleukemic response were observed in either species.