A genomic library ofClostridiumthermocellum DSM 1237 was constructed in a bacteriophage lambda vector and screened for hydrolysis of carboxymethyl cellulose (CMC), lichenan and methylumbelliferyl-β-glucoside. Recombinant clones expressing four β-glucanases and two distinct β-glucosidases were obtained. The β-glucanase activities could be classified with respect to their substrate specificities as β-1, 4-endoglucanase (CMCase), β-1, 3-endoglucanase (laminarinase), and β-1, 3-1, 4-endoglucanases (lichenanase). The β-glucosidases were identified as cellobiases hydrolyzing both aryl-β-glucosides and cellobiose.