The strictly anaerobic faecal flora of patients with Crohn's disease (CD) contains higher numbers of coccoid rods (Eubacterium, Peptostreptococcus and Coprococcus species) and gram-negative rods (Bacteroides vulgatus) than the flora of healthy subjects. The abnormal flora of patients with CD might affect levels of glycolytic enzymes and metabolic products and thus play some role in the pathogenesis of CD. Therefore, the activity of 23 glycosidases that can degrade mucus glycoproteins or plant polysaccharides, in faeces of patients with CD was compared with healthy subjects. Total enzyme activity in faecal samples of patients with CD was significantly higher than in healthy subjects, but statistically the activity of individual enzymes did not significantly differ. Faecal glycosidase activity is predominantly of bacterial origin since glycosidase activity was absent or very low in faeces of germ-free rats.