Nodules are concentrated in water depths of 4500-5500m near the calcite compensation depth in parts of four deep-sea basins formed on Cretaceous crust. Nodules occur at 80% of stations in the SW Pacific and S Penrhyn basins and 70% of stations in the N Penrhyn and E central Pacific basins. Major variations in nodule concentrations and grades, apparently largely controlled by plankton productivity, fall into three broad latitudinal zones. The usual inverse relationship of nodule concentrations and grades appears to apply generally. -from Author