Two glycoside hydrolase (GH) families were analyzed to detect the presence of functional divergence using the program DIVERGE. These two families, GH7 and GH16, each contain members related by amino acid sequence similarity, retaining hydrolytic mechanisms, and catalytic residue identity. GH7 and GH16 comprise GH Clan B, with a shared beta-jelly roll topology and mechanism. GH7 contains fungal cellobiohydrolases and endoglucanases and is divided into five main subfamilies, four of the former and one of the latter. Cluster comparisons between three of the cellobiohydrolase subfamilies and the endoglucanase subfamily identified specific amino acid residues that play a role in the functional divergence between the two enzyme types. GH16 contains subfamilies of bacterial agarases, xyloglucosyl transferases, 1,3-beta-D-glucanases, lichenases, and other enzymes with various substrate specificities and product profiles. Four cluster comparisons between these four main subfamilies again have identified amino acid residues involved in functional divergence between the subfamilies. (c) 2009 Wiley Periodicals, Inc. Biopolymers 91: 478-495, 2009.