Toluene diisocyanate (TDI) is widely used in the manufacture of polyurethanes and is a recognized cause of occupational asthma. Although extensive investigations have been undertaken, the molecular mechanism(s) of the disease is still unclear. We hypothesized that inflammatory cytokines are required during both the sensitization and elicitation phases of the disease and have utilized TNF-R knock-out (KO) mice to address the hypothesis. Black C57 TNFR knock-out mice were exposed to TDI by sc injection and challenged by inhalation of 100 ppb TDI vapor. Control animals included: wild type C57 animals, sham-exposed animals that were challenged with TDI, and animals that were injected with anti-TNF antibodies prior to sensitization and again prior to challenge. Total IgE was increased in the knock-out animals compared with the wild type sensitized and challenged animals whereas TDI-specific IgG antibodies did not differ significantly in KO and wild type animals. There was less inflammation in the nares and trachea in KO animals compared with the wild type animals exposed to TD1 as well as less goblet cell hyperplasia and epithelial damage. Airway reactivity was assessed in animals treated with anti-TNF$alpha$ antibody and found to be substantially reduced compared with that in sensitized and challenged animals. These results indicate that TNF$alpha$ plays a role in the immunologic and physiologic responses and in airways inflammation in this animal model and suggests a role for TNF in occupational asthma due to TDI.