An identification and quantitative analysis was made of the fungi, thermophilic actinomycetes, bacteria, insects, and mites present in respirable dust and bulk dust samples collected in grain elevators in the Duluth/Superior area. Respirable dust samples were taken with personal air samplers for over 250 grain elevator workers during standard work shifts. Collections of the dust were made in October and November of 1977. Grains examined included spring wheat, barley, durum wheat, oats, sunflower, flax, rye, corn and mixed. The most prevalent microorganisms in airborne grain dust were bacteria, accounting for half of the total. Species of yeast, Aspergillus, Penicillium, and Ustilago made up one fifth of the fungi present. Of the various job classifications present, annex workers were exposed to the highest concentrations, and supervisors, the least. Use of scanning electron microscopy proved to be important in assessing the health hazards of grain dust totally. Bulk grain and settled grain dust samples contained very few whole insects, mites or insect fragments. Insects fragments were generally from the Orthoptera or Coleoptera orders, while whole insects were usually common storage insects. The concentrations of spores were higher for grain workers than for samples from a comparison group of city workers.