INTRODUCTION This study@ conducted for the American Petroleum Institute@ was designed to assess the effect of benzene administered to seven species of animals by inhalation six hours per day@ five days per week at an exposure level of 300 parts per million (ppm) for twelve weeks. The guinea pigs were exposed for an additional five day period@ six hours per day during Week 37 at an exposure concentration of 800 ppm. Hematology tests were performed on all species and differential bone marrow counts were performed on all species except guinea pigs. Necropsy examinations were performed at Week 12 (on all rats@ rabbits@ cats@ dogs@ monkeys@ and half of the mice)@ at Week 16 (on the remaining mice)@ and at Week 104 (on all guinea pigs).