Environmental agents responsible for pulmonary dysfunction in poultry workers who came into direct contact with live chickens are reviewed. Sources of risk include skin debris from the epidermis of birds, aerosolized feed, nuisance dust particles, broken feather particles, and immunogenic agents localized on house litter, poultry excreta, feathers, and skin surface. Four cases of hypersensitivity pneumonitis in patients whose exposure to chickens was implicated as the causal factor are described. A survey of 205 subjects in the turkey industry is reported in which 69 percent of the workers described at least one respiratory symptom, although only 14 percent of these workers demonstrated circulating antibodies to turkey serum. The contribution of gram negative bacteria or their endotoxins to the development of hypersensitivity pneumonitis is reviewed. Studies in which worker exposure to gram negative bacterial endotoxins caused fever, eye irritation, diarrhea, fatigue, nausea, cough, nasal irritation, chest tightness, and phlegm are described. Dust samples and aerosols in poultry processing and confinement areas are reported to contain high concentrations of endotoxins. Several studies of high bacterial counts found in the air of poultry factories are cited. The potential threat of exposure to bacterial strains resistant to tetracycline (60548), streptomycin (57921), furazolidone (67458), and sulfathiazole (72140) is described. The authors conclude that poultry workers are at risk due to exposure to high concentrations of dust containing viable bacteria, gram negative endotoxins, and immunologic agents. It is hoped that control measures will be taken to maintain airborne exposures to concentrations that are safe.