The toxicity and inflammatory potential of spring wheat, oat, corn, and flax seed were assessed. Extracts of grain dust were analyzed through quantification of gram negative bacterial endotoxin and protein contents, chemotaxis for purified human polymorphonuclear leukocytes, and several alveolar macrophage functions. The latter included release of lactate-dehydrogenase, phagocytosis, macromolecular synthesis, and interleukin-1 production. Extracts of all four grain dusts impaired protein synthesis and decreased phagocytosis of rat alveolar macrophages at 7.5 to 25 milligrams per milliliter. Interleukin-1 production was stimulated from 3.8 to 14.3 fold over controls. Activity of the grain dust extracts did not correlate with endotoxin content. The authors conclude that extracts of the four selected grain dusts produce ill effects in rat alveolar macrophages in-vitro and may be a potential hazard to agricultural workers exposed to grain dust. Further studies on grain dust induced diseases are needed to develop and implement control measures to minimize the occurrence of occupational lung disease.