The redox potentials of strictly analogous complexes of molybdenum and tungsten were studied using temperature dependent electrochemistry in order to evaluate a proposed influence of the potentials on the use of tungsten at thermophilic conditions and the use of molybdenum at mesophilic conditions in the molybdopterin dependent oxido reductases. Each pair of molybdenum and tungsten compounds was studied under identical conditions. The studies reveal that tungsten's redox potential is always more temperature sensitive than molybdenum's with a stronger shift of the potential upon temperature change in negative or positive direction depending on the ligand system. No exceptions to this different behaviour of molybdenum and tungsten were observed. The conducted experiments are described in detail and the relevance for the use of either metal is discussed. In addition a possible reason for this fundamental difference as part of the nature of molybdenum and tungsten is proposed.