Homogeneous Fe and Mn oxidation catalysts can be immobilized on silica, zeolites, clays, layered double hydroxides and polymers. In addition to the well-known porphyrin catalysts, there is increasing interest in complexes with non-planar ligands. Based on a selection of examples, this paper discusses heterogenization methods, and the effects of heterogenization on the catalytic activity. (C) 2000 Elsevier Science B.V. All rights reserved.