Total and respirable airborne dusts produced by cotton carding, poultry confinement, poultry processing, and silo unloading operations were analyzed for the presence of gram negative bacterial endotoxins. Dust samples were collected at the facilities using various filters. Sterile non pyrogenic plastic ware was employed during gram negative bacterial endotoxin assays. Quantification of the endotoxins present in supernatant fluids obtained via the decantation and centrifugal treatment of the samples was performed using a spectrophotometric modification of the amebocyte lysate gel test. The resulting turbidity was quantified as the apparent increase in absorbance at 360 nanometers (nm). Results were analyzed by linear regression, were compared to a standard curve, and were reported in terms of the US Reference Endotoxin. Blank unused filters, similarly treated, served as negative controls for each source and type of dust collected. Quantifiable endotoxins were found in every dust sample analyzed. The highest concentration of endotoxin contamination, 187 nanograms per milligram (ng/mg), was found in poultry processing facility samples, while the least contaminated total dust (11ng/mg) was obtained from poultry confinement samples. Total dust with an endotoxin content of 167ng/mg resulted from cotton carding operations, while silo unloading generated 87ng/mg. Gram negative endotoxin sources varied widely, having a fecal origin in poultry related samples and being caused by the presence of field and storage organisms in cotton and silage samples. Both total and respirable dusts were contaminated with endotoxins that had the capability of reaching alveolar spaces in the lungs. The author recommends that the potential biological effects of inhaled dusts must be considered, together with gravimetric dust burdens, in occupational environments.