Metal targets have been bombarded with cesium and hydrogen ions in the energy range 100 to 1000 eV. Angular and energy distributions and the yield of the H− ions have been measured as function of energy and ion mix. Synergistic effects due to simultaneous hydrogen and cesium ion bombardment produce a higher H− yield than the sum of the individual processes. Cesium coverage on metal surfaces due to cesium ion bombardment has been studied. High coverages corresponding to a workfunction of 1.6 eV can be obtained at 100 eV energy when the target mass is smaller than the cesium mass.