Controlled pore glass was activated by transition metal salts, FeCl 2, FeCl 3, VCl 3 and ZrCl 4, and derivatized by the method of Cabral et al. 1 Glucoamylase (exo-1,4-α- d-glucosidase, EC 3.2.3.1) was coupled to the aldehyde derivative, the resulting initial activities being 61.7, 71.8, 57.6 and 63.2 U g −1 of matrix, respectively. The immobilized glucoamylase preparations in which the carrier was activated with zirconium (IV) chloride displayed a very stable behaviour, with a half-life of 1709 h, in contrast with the preparations activated with iron(II) chloride ( t 1 2 = 43 7 h , iron(III) chloride ( t 1 2 = 518 h ) and vanadium(III) chloride ( t 1 2 = 893 h ). Several biocatalysts, fungal α-amylase (EC 3.2.1.1), bacterial α-amylase (EC 3.2.1.1), β- d-fructofuranosidase (invertase, EC 3.2.1.26), papain (EC 3.4.22.2) and yeast cells of Saccharomyces cerevisiae with β- d-fructofuranosidase activity were immobilized on aldehyde derivatives of titanium(IV)-activated porous silica (Spherosil), half-lives of 140, 157, 980, 236 and 413 h being obtained, respectively.