The binding states and desorption kinetics of hydrogen and nitrogen on the (100) plane of Mo are examined by flash desorption mass spectrometry, and the results are compared with the adsorption of these gases on (100) W. Since molybdenum and tungsten are isoelectronic and have the same crystal structure and lattice constant, differences must be attributed to differences in the electronic properties of the substrates. It is found that, while there is a good correlation between the binding states of these gases and between the binding states of each gas on the substrates, there are several interesting differences. There is an extra binding state observed for hydrogen on (100)Mo which is not observed on (100)W. It is suggested that this state may also exist on (100)W but not be observed in flash desorption. It is also found that there are significant differences between the binding energies on the substrates. Hydrogen is much more strongly bound on W while nitrogen is more strongly bound on Mo. The difference in hydrogen adsorption is interpreted in terms of the greater bonding capabilities of the 5d vs. 4d electrons of the substrates, while the strength of the nitrogen adsorption bond on Mo is attributed to the lateral interaction in the plane of the substrates which should be stronger for Mo than for W.(1) This work partially supported by ARPA under Grant DAHC15-69-G6.(2) (a)