This paper reviews a series of studies published recently on silicate, aluminosilicate, and niobosilicate micro- and mesoporous molecular sieves modified with transition metals (Cu, Fe, V). These metals were incorporated during the synthesis or in the post-synthesis procedures (impregnation, ion exchange, chemical vapour deposition, immobilisation of organic complex). In case of niobosilicate matrix, the strong interaction between the included metal and niobium species was detected by electron spin resonance spectroscopy (ESR) investigation. The reducibility of metal species in relation to the structure and composition of matrix is discussed. The results of the adsorption of probe molecules (NO, CO, SO2) are shown and discussed. (c) 2006 Elsevier B.V. All rights reserved.