Endotoxin (or lipopolysaccharide [LPS]) is a potent inflammatory stimulant which is found in ambient air in occupational settings. Asthma in the workplace is an increasingly significant problem. Asthma is characterized by airway inflammation and increased reactivity to both allergic and non-allergic stimuli. LPS is known to induced airway inflammation in normal subjects and to enhance airway reactivity in asthmatics. Additionally, both alveolar macrophages and mononuclear cells from asthmatics secrete higher amounts of cytokines (interleukins 1 and 8 [IL-1, IL-8] and granulocyte macrophage-colony stimulating factor [GM-CSF] ) than those from normals. Thus, it is likely that LPS enhances allergen-induced inflammation and that allergic asthmatics are more sensitive to the effects of LPS. Preliminary data show that exposure to low levels (250 ng/m3) of LPS at risk for four hours enhances both immediate responsiveness to inhaled allergen and allergen-induced eosinophils as observed in induced sputum. In the nasal airways of allergics, a single dose of 1,000 nanograms of LPS enhances polymorphonuclear leukocyte influx associated with allergen challenge. This latter finding also correlates well with baseline IL-8 and ECP levels, suggesting that constitutive airway inflammation enhances response to these stimuli.