The paper summarizes the results of FTIR studies of specific properties of zeolites, compared with metal oxides, in the adsorption of simple molecules. An attempt is made to explain the unusual properties of zeolites, such as linkage isomerism of adsorbed CO, extremely high Lewis acidity of exchangeble cations, Brønsted acidity of H-zeolites and basicity of zeolite framework oxygen atoms. Acidity of zeolitic hydroxyl groups, choice of test molecules for acid and basic sites, advantages of carbon monoxide and fluoro form for testing the strength of surface centers, correlation between their frequency shifts and absorbance are discussed, as well as the influence of environment upon the electron- accepting properties of cations and their ability for isomerism.