The protease which initiates the rapid protein degradation during germination of Bacillus megaterium spores was synthesized during sporulation as a Mr = 46,000 polypeptide (P46) which was found in the developing forespore. P46 was processed during sporulation to a Mr = 41,000 species (P41) 2-3 h after P46 synthesis and at the time of or slightly before accumulation of dipicolinic acid. P41 was the predominant form of the protease in the dormant spore, with smaller amounts of unprocessed P46. In the first minutes of spore germination P41 was processed (t1/2 less than 10 min) to a Mr = 40,000 species (P40), which appeared identical to the subunit of the purified active enzyme. The latter processing reaction did not require metabolic energy, but P40 disappeared completely during further germination (t1/2 approximately 40 min) in a reaction which did require metabolic energy. It seems probable that precursors P46 and P41 of the spore protease are involved in the regulation of the activity of this spore enzyme.