Divinylbenzene (DVB) is a crosslinking monomer used primarily for copolymerization with styrene to produce ion-exchange resins. The toxicity of inhaled DVB was investigated because of the potential for worker exposure and the structural similarity of DVB to styrene, a potential carcinogen. Male and female B6C3F1 mice were exposed to 0, 25, 50, or 75 ppm DVB for 6 hr/day, 5 days/week for up to 2 weeks. Six mice/sex/dose group were killed after 3, 5, and 10 exposures and six mice/sex in the 75 ppm group were killed 7 days after 10 exposures. The most severe effects occurred in the nasal cavity and liver, with less severe effects occurring in the kidneys. In the nasal cavity olfactory epithelium acute necrosis and inflammation were present at early time points followed by regeneration, architectural reorganization, and focal respiratory metaplasia by 7 days after the last exposure. Olfactory epithelial changes were concentration-dependent with extensive involvement at 75 ppm and peripheral sparing at 25 ppm. There was also necrosis and regeneration of olfactory-associated Bowman's glands as well as the lateral nasal (Steno's) glands. Hepatocellular centrilobular (CL) necrosis was observed only in the 75 ppm dose group and was similar to that caused by styrene. A time-dependent progression was observed, characterized by CL degeneration after 1 exposure, necrosis after 3 and 5 exposures, and chronic inflammation with CL karyomegaly after 10 exposures and 7 days after the 10th exposure. Hepatic GSH levels were decreased in a dose-dependent manner. In the kidneys, transient tubular damage was observed in some male mice exposed to 75 ppm, and appeared to be a response to DVB-induced tubular epithelial injury. Divinylbenzene (DVB; CAS No. 1321-74-0) is a specialty monomer used for producing vinyl polymers. The toxicity of inhaled DVB was investigated because of the potential for worker exposure and the structural similarity of DVB to styrene, a potential human carcinogen (IARC, 1987). The bifunctionality conferred by the two vinyl groups makes DVB a highly reactive crosslinking agent and may also contribute to its toxicity. Occupational exposure to DVB occurs primarily by inhalation and dermal contact and consequently DVB is an irritant to the eyes and respiratory system (Clayton and Clayton, 1981). The current Occupational Safety and Health Administration threshold limit value (8-hr timeweighted average) for DVB is 10 ppm (ACGLH, 1994).Divinylbenzene monomer is manufactured by dehydrogenation of mixed isomeric diethylbenzenes. After removal of light by-products, the product is recovered as a mixture of m-and /?-DVB and m-and /7-ethylvinylbenzene (EVB), the partial dehydrogenation product. Because the DVB monomer readily polymerizes to a brittle, insoluble resin, it is heavily inhibited with tert-butyl catechol and diluted with EVB to minimize this reaction. Three commercial grades of DVB are produced containing approximately 22% (DVB-22), 55% (DVB-55), and 80% (DVB-80) DVB.By far, the greatest use of DVB is as a cross-l...