A series of experiments has been conducted to explore the effects of electrolyzing heavy water (D2O) using palladium and platinum electrodes. Over 40 weeks of experimental runs have been conducted in four cells which electrolyze heavy water using palladium and platinum electrodes. Tritium production, neutron and gamma radiation, and cell temperatures were monitored simultaneously and continuously throughout the runs. These experiments have resulted in seven elevated temperature events similar to those claimed by Pons and Fleischmann, with no correlating detection of nuclear products. The seven events which have occurred to date all take the same general form in which the apparent heat output of a cell, as seen in terms of the change in cell fluid temperature, increases in a distinct and significant step. A single light water cells, identical in all respects to those using heavy water, has been operated for over 15 weeks and has produced no temperature excursions, and also no nuclear products.