The electrolytic insertion of deuterium into Pd at 95 degrees C was investigated by a simple calorimetric technique. This involved continuous feeding of heating power to the electrolytic cell to maintain it isothermal with an external thermostatic bath : any extraneous thermal phenomenon taking place inside the cell is directly determined by the lack of balance of the original heating power input. It was thus found that Pd loading by deuterium is always paralleled by excess power generation, which largely exceeds the electrolytic power input. After prolonged electrolysis the loaded electrodes were found to continue heat generation in open circuit (o.c.) conditions. The reproducibility of the thermal phenomenon allowed its dependence on several experimental parameters to be investigated.