The　coupling　with　external　mechanical　systems　such　as　oscillating　masses　working　as　tuned　mass　dampers,　dynamic　mass　absorbers,　elasto-plastic　dampers,　and　rigid　walls　is　an　effective　method　to　reduce　the　displacements　and　drifts　of　structures　under　external　loads.　An　alternative　method　is　provided　by　the　coupling　of　the　structure　with　an　independent,　auxiliary　elasto-plastic　system.　This　paper　investigates　the　dynamic　and　seismic　behaviour　of　a　structure　rigidly　coupled　with　an　auxiliary　yielding　mechanical　system　under　harmonic　and　seismic　ground　excitation.　A　two-degree-of-freedom　model　is　used　to　describe　the　dynamic　and　seismic　behaviour　of　the　main　structure　rigidly　coupled　to　the　yielding　system,　which　is　described　by　a　one-degree-of-freedom　model.　The　auxiliary　system　has　an　elasto-plastic　constitutive　behaviour　that　is　modelled　by　a　Bouc-Wen　model.　The　equations　of　motion　of　the　coupled　system　are　obtained　by　a　direct　approach.　The　coupling　with　the　yielding　system　is　considered　beneficial　if　the　displacements　of　the　coupled　system　reduce　with　respect　to　those　of　the　stand-alone　frame　structure.　An　extensive　parametric　analysis　is　performed　to　point　out　the　role　of　the　mechanical　parameters　that　describe　the　elasto-plastic　constitutive　behaviour　of　the　auxiliary　system.　Results　reveal　that　in　large　ranges　of　the　parameters＇　values,　the　coupling　with　the　elasto-plastic　system　improves　the　performance　of　the　frame　structure.