Treating a simple liquid metal as a dense two-component plasma consisting of ions and electrons, we derive a rather general screened interionic potential within the framework of the thermodynamic Green function technique. The resulting potential incorporates both ions and electrons into the screening and contains pseudopotential terms of any order. Similar to Hubbard for the electrons, we derive also a static ion local-field correction which accounts for ion—ion correlation effects in the Montroll—Ward approximation. The interionic potential in the case of liquid Cs is strongly modified in comparison with the effective potential derived within second-order pseudopotential theory.