The chitinase- and β-N-acetylglucosaminidase(GlcNAcase)-producing ability of intestinal bacteria from Pinnipedian animals was determined using fluorogenic 4-methylumbelliferone glycosides of N-acetylglucosamine oligosaccharides. Intestinal microflora of a single Cape fur seal, three California sea lions and three South American sea lions were characterized by a predominance of isolates of the Bacteroidaceae and Enterobacteriaceae families and the genus Clostridium. Of the 711 isolates tested 26.0, 10.0 and 8.7% could hydrolyse 4-MU(GlcNAc)1 4-MU(GlcNAc)2, and 4-MU(GlcNAc)3, respectively. This result suggests that β-GlcNAcase producers occur at a higher density than do chitinase producers. Moreover, β-GlcNAcase, and to a lesser degree, chitinase seem to be efficiently produced by facultative anaerobes in the Cape fur seal and the California sea lion, and by both facultative and obligate anaerobes in the South American sea lion. To our knowledge, this is the first paper to report that isolates of the family Bacteroidaceae and the genus Streptococcus produce chitinase and/or β-GlcNAcase.