An investigation of the electrolytic loading of hydrogen and deuterium into palladium cathodes was undertaken using in-situ measurement of the cathode resistance to determine the resultant hydride and deuteride stoichiometries. Conventional D/Pd loading ratios between 0.75 and 0.82 were obtained for palladium cathodes that had been subject to minimal pretreatment. These loading levels were essentially independent of electrolyte composition and pH, or of the source or purity of the palladium, but increased with current density. The H/Pd loading ratios observed in light water experiments were found to be 6%-10% higher than the D/Pd ratios obtained during heavy water electrolysis. Much higher D/Pd loading ratios of between 0.91 and 0.93 could be achieved routinely providing that the electrodes were first vacuum annealed and etched with acid. These results support the claims of McKubre and coworkers that classical loadings of 0.75-0.85 can be exceeded using electrolysis in D2O with palladium cathodes at room temperatures. This finding has particular importance in view of a number of recent experiments which suggest that excess heat and/or nuclear product generation in the Pd + D system occurs only when the loading ratio exceeds 0.90.