The reactions of hydrogen atoms, generated by ultraviolet photolysis of hydrogen iodide, with solid ethane and propane at 10 K are investigated using electron spin resonance (ESR) to identify the reaction products. Although the results are generally similar to those found by others for these tunneling hydrogen abstraction reactions in dilute solutions of the alkanes in xenon, there also are significant differences, most notably, evidence that only the secondary hydrogen of propane is abstracted in its tunneling reaction with an. H atom. Also notable is the high degree of crystalline order in the ethane matrix, which is preserved in the ethyl radical product of the H atom-ethane reaction.