Earth rotation parameters (ERP) are measuredwith very high accuracy. Changes in the ERP originate in movements ofmass within the Earth system. Therefore, these changes can be used todistinguish the eustatic from the steric effects in sea levelchange. We were able to assimilate measured ERP into a globalcirculation model of the oceans. On interannual timescales the modelshows realistic behaviour and succeeds in the reproduction of the ERPobservations. The biggest impact here is on the total ocean massvariation. By simultaneous assimilation of oceanographic data as SSHand SST in addition to ERP conclusions about the ocean heat contentcould be drawn.