Experimental and epidemiological studies indicate that inhalation of organic dust containing-endotoxin and endotoxin, as a separate and independent component, have a beneficial effect against cancer, specifically lung cancer. Organic dust, cotton dust, contains gram negative bacteria in a relatively high concentration. Gram negative bacteria are the source of endotoxin in organic dust.  Aerosolization of cotton dust using a generation system results in large concentrations of airborne microbes, with about a three log reduction from the raw material. Microbes appear to be some what evenly disbursed among a wide variety of particle size ranges.  Animals (mice – C57BL/6J) injected with metastatic tumor cells (Lewis Lung) and treated with aerosolized cotton dust and endotoxin have an increased survival time as compared with controls.  These data indicate that endotoxin has a beneficial effect against tumors. Animals treated with an inert dust (cellulose dust) did not have any difference for survival when compared to controls suggesting that irritation or inflammation from the dust is not responsible for the increased survival in animals treated with cotton dust. These experimental data support epidemiological studies of various occupational groups (cotton textile, agricultural and automobile machinery workers) who are exposed to endotoxin and experience a  reduced rate of lung cancer. Recently, reduced cancer rates in cotton textile workers have been reported for liver and “gastrointestinal” cancer, suggesting that a benefit of exposure may be occurring in other organ sites besides the lung. The animal data support the suggestion that reduced smoking rates in study populations and the healthy worker effect are not responsible for observed lower than expected rates of cancer in various occupational groups. A brief review of epidemiological findings related to reduced lung cancer rates and exposure to organic dust is presented. Recent epidemiological studies support animal investigations of a benefit from exposure. It has been proposed that there are a large number of occupational groups experiencing benefits of exposure and reduced cancer rates. Mechanisms for the anti-cancer effects of endotoxin are also discussed. Overall, it appears that certain occupational groups that are exposed to endotoxin are experiencing a beneficial effect from exposure.