Recent studies of epitaxic films of PbSe have shown that atomic hydrogen, H, and oxygen, O2, produce changes in their electrical properties. To clarify the sorption phenomena, a study of the kinetics at room temperature was undertaken on as-grown films of different thicknesses. Analysis of the results has shown that O2 has a marked surface effect and also slowly diffuses into PbSe films; H diffuses substantial distances up to 2; approximately 1018 Pb and Se vacancies/cm3 exist in the as-grown PbSe films. Temperature measurements confirm that the activation energy for the H diffusion is close to 0.3 eV. The agreement between various measurements supports recent conjectures by Pratt and Parada on the nature of vacancies in the lead salts as well as Holloway and Logothetis on compensation in these materials.