We propose that thed-d fusion rate in palladium can be enhanced by the combined screening of the electrostatic interactions by the itinerant deuterons and the conduction electrons. The model assumes that, under certain conditions, deuterium exists as a D+ ion in palladium. The combined screening by electrons and the D+ ions (deuterons) is found to be more effective than that due to electrons alone. The calculated values of thed-d fusion rates, considering screening, for composition PdD at 300 K are 10−16 s−1 and 10−14 s−1 for D2+ ion and D2 molecule respectively. These values lie in the range suggested by the recent electrochemical experiments.