Maleic anhydride is a white, crystalline solid with a sharp, irritating odor. The primary method of manufacture is based on the reaction between benzene vapor and air in the presence of a vanadium catalyst; and it is used to manufacture phthalic anhydride, esters, polyester resins, dye intermediates, pharmaceuticals, agricultural chemicals, and fumaric acid. Maleic anhydride dust or vapor is an acute skin, eye, and respiratory tract irritant at concentrations of about 2 ppm. The primary emission sources in descending order are phthalic anhydride production, maleic anhydride production, end product manufacture, and packaging losses. Control of maleic anhydride emissions can be effected by scrubbing the uncondensed portion of the reactor effluent after it passes through a partial condenser. This is done principally to recover maleic anhydride. Scrubbing is also used to control particulate emissions from flaking, tableting, and packaging operations with efficiencies of at least 98 percent. A number of other techniques are under development for controlling maleic anhydride emissions. Based on the results of the health effects research presented in this report, and the ambient concentration estimates, it is possible that maleic anhydride as an air pollutant might pose a threat to the health of the general population.