INTRODUCTION: This study@ conducted for the American Petroleum Institute@ was designed to assess the toxicity of commercial hexane when administered by whole-body inhalation as a respirable vapor to 60 Fischer 344 rats (IO/sex/group) and 60 B6C3Fl mice (la/sex/group). Twenty rats (la/sex/group) and 20 mice (la/sex/group) were exposed to room air and nitrogen. The test substance was administered for 6 hours per day@ 5 days per week@ for 13 weeks at target concentrations of 0@ 900@ 3@000 and 9@000 parts per million (ppm). Exposures commenced in staggered groups by species beginning on 10 April 1989 for the rats and 11 April 1989 for the mice@ and were completed on 12 July 1989 for the rats and 13 July 1989 for the mice.