The relative rates of cell division in different regions of the pea shoot apical meristem were obtained by measuring the increase in the numbers of metaphases following application of colchicine to the plants. Absolute values for the rates of cell division could be calculated since the average rate of cell division for the whole apex was known. Measurements of the rates of cell division were obtained at defined intervals during the course of a single plastochron. Within each region of the apex the rate of cell division did not change more than about two-fold throughout the plastochron. There was very little or no increase in the rate of cell division associated with leaf initiation. The formation of a leaf primordium and the subsequent growth of the apical dome apparently result from changes in the direction of growth rather than changes in the rates of growth. Three main regions were discernible within the apical meristem: a region with a slow rate of cell division in the apical dome, a region of a faster rate of cell division at the base of the apical dome and at the site of initiation of procambial strands, and a region of an intermediate rate of cell division in the newly initiated leaf primordium and the adjacent part of the shoot axis.