Electron microscopy of thin-sectioned and freeze-etched cells of Sporosarcina ureae demonstrated that division occurred in two or three perpendicular planes. The complex wall consisted of a 12-nm-thick amorphous layer which was adjacent to the plasma membrane (PM) and an overlying 16-nm-thick poroteinaceous array (a regularly structured (RS) layer). Septation proceeded with the ingrowth of the PM and the inner layer in association with division mesosomes. The RS layer remained behind at the initiation site, and buckled and sloughed off to accommodate its continued extension. After the septal annulus had fused, perpendicular septa were initiated. As these secondary septa proceeded to form a tetrad of cells, the RS layer began a gradual peripheral ingrowth along the first division plane. Separation of the cells was incomplete until the centripetal growth of the RS layer had finished; often this was not until a packet of eight cells had been formed.