The kinetics of adsorption and abstraction for the system H (D) on Al(100) has been investigated using an efficient atomic beam source, thermal desorption spectroscope and multiplexed mass spectrometry. Emphasis was put on the quantitative determination of the reaction parameters. The initial sticking coefficient for atomic hydrogen and atomic deuterium is 0.6; the saturation coverage is 1.6 monolayers. On the D(H) saturated surface, abstraction takes place at a surface temperature of 150 K due to impinging H (D) atoms (H+D→HD) with an abstraction coefficient of 0.4 D/H. No significant isotope effect can be observed. The abstraction process cannot be described by a direct Eley-Rideal mechanism, but rather by a hot-precursor mechanism. In addition to abstraction, about 10% of the adsorbed species are removed from the surface by a collision-induced associative desorption process.