Dehydration and adsorption effects on the parameters of thermally stimulated exoemission (TSE) from ceramic samples of BeO are investigated. Adsorption of active gases increase the emissivity of BeO if it is dehydrated by thermovacuum treatment. For the original hydrated sample the adsorption results in a small decrease of TSE intensity. For recombination proceeding in the mobile surface layer it is necessary that it should have some optimum concentration of adsorbed particles. It is an explanation for the data obtained.