Phthalic anhydride is a white, crystalline solid with a characteristic choking odor. It is produced by the oxidation of either naphthalene or ortho-xylene, and it is a key industrial intermediate in the manufacture of resins, polyesters, dyes, and plasticizers. The major acute toxic effect of exposure to phthalic anhydride dust or vapor is its irritating action on the skin, eyes, and mucous membranes. The primary end use is the manufacture of plasticizers, with polyester resin production second. The major emission sources in descending order are product storage, manufacturing, end product manufacturing, and product handling. Scrubbers and incinerators are currently being used by industry to control phthalic anhydride emissions with efficiencies of 86 and 99 percent, respectively. Currently used practices to control the continuous gaseous effluent are the use of knock-out pots for removal of solid phthalic anhydride and the venting of storage tanks to the main process vent gas incinerator. Based on the results of the health effects research presented in this report, and the ambient concentration estimates, phthalic anhydride as an air pollutant apparently does not pose a threat to the health of the general population. In addition, phthalic anhydride does not appear to pose other environmental insults which would warrant further investigation or restriction of its use at the present time.