Arsenic, antimony, and germanium films laid down on glass surfaces by decomposition of the hydrides have been studied from the standpoint of reaction kinetics in three sets of reactions: the decomposition of hydrides and deuterides, the interaction of hydrides and molecular deuterium, and the exchange reaction of hydrogen and deuterium. Only in the first of these have the surfaces marked catalytic activity. The orders of reaction and the activation energies have been determined. The accelerated catalytic influence of foreign elements, notably antimony in arsine decomposition, has been established. The results obtained contrast strikingly with the properties of clean filaments and evaporated films among the transition elements. The results emphasize the basic importance of chemical factors and de-emphasize the importance of surface cleanliness as a controlling factor in problems of chemisorption and surface catalysis.