Xylene is a colorless, flammable liquid having an aromatic odor similar to that of benzene and toluene. There are three isomers of xylene: ortho-, meta-, and para-xylene. Data linking ortho-xylene exposure with health effects are lacking, due to the almost always concomitant benzene and toluene. Ortho-xylene is an irritant and narcotic at high concentrations, producing effects similar to alcohol intoxication. The primary emission sources in descending order are mixed xylene solvent usage, mixed xylene production, ortho-xylene production and solvent usage, and bulk storage. Total emissions are estimated to have been about 184 million pounds in 1974. Although emission controls specifically for ortho-xylene are not reported, two types of controls are used extensively by the chemical industry to control hydrocarbon emissions. These are vapor recovery and incineration. Control by adsorption on activated charcoal is used when recovery is economically desirable. Based on the results of the health effects research presented in this report, and the ambient concentration estimates, it appears that ortho-xylene as an air pollutant does not pose a threat to the health of the general population. In addition, ortho-xylene does not appear to pose other environmental insults which would warrant further investigation or restriction of its use at the present time.