Information on the life cycle of the soil fungus S. griseus in submerged cultures is described and also illustrated with photomicrographs. The spores first germinated and produced profuse vegetative mycelium. Vacuolation, autolysis, and fragmentation of the mycelium was evident during fermentation in deep cultures, accompanied usually by formation of large numbers of spores. Submerged spores could be produced in a shorter time and in much larger quantities than spores produced on the aerial mycelium on the surface of solid or liquid media. The production of these spores for the purpose of seeding large tanks may be advantageous. The mycelial fragments may germinate at any place by one to several germ tubes, similar to those produced by the spores. The spores produced in submerged cultures were smooth and wettable. The physiological and morphological characteristics of submerged spores and of the aerial spores produced on the mycelium on solid or liquid media were similar. All the S. griseus cultures, as other species of Streptomyces studied, produced spores in submerged cultures in synthetic and organic media. Some differences were found among strains in regard to the time and amount of sporulation. Colonies of S. griseus, submerged in nutrient agar, produced a large number of spores within 2-12 days at room temp.