Mutations affecting quantitatively the production of the sporulation-associated extracellular alkaline protease were isolated and characterized. They fall into at least five genes, three of which, ScoA, B and C, were mapped in the argC-metC region. The pleiotropic effects of these mutations concern several or all of the following: rate and timing of protease production, synthesis of alkaline phosphatase, time-course of spore formation. Electron microscopic evidence indicates delayed switch from one morphological stage to another. The nature of the Sco mutations and the genetic regulation of sporulation are discussed.