The update criteria and recommendations for a revised benzene standard to that of August 1976 are given. NIOSH considers the accumulated evidence from clinical as well as from epidemiologic data to be conclusive at this time that benzene is leukemogenic. Because it causes progressive, malignant disease of the blood- forming organs, NIOSH recommends that, for regulatory purposes, benzene be considered carcinogenic in man. Since there is no exposure level which is considered to be without danger, NIOSH recommends that exposure to benzene be kept as low as possible, that benzene not be used as a solvent or diluent in open operations and that product substitution should be a paramount consideration. NIOSH recommends that occupational exposure be controlled so that no worker will be exposed to benzene in excess of 1 ppm (3.2 milligrams per cubic meter) in air as determined by an air sample collected at 1 liter/minute for two hours.