Tomato stem extracts released glucose, N-acetylglucosamine and other reducing groups from hyphal walls of the wilt pathogen Verticillium albo-atrum during in vitro hydrolysis. Extracts from V. albo-atrum infected stems contained more l,3-β-glucanase, chitinase, β-glucosidase and N-acetyl-glucosaminidase and were more active on purified preparations of mycelial cell wall than were those from healthy stem. Stem extracts from the infected susceptible tomato cv. Craigella contained more activity than extracts from an infected isogenic resistant line. Purified chitinases from both tomato and V. albo-atrumreleased N-acetylglucosamine from hyphal walls. Neither the tomato endo-l,3-β-glucanase nor the exo-1,3-β-glucanase and β-glucosidase from V. albo-atrum, showed activity individually towards the hyphal wall but mixed enzyme digests containing tomato endo-1,3-β-glucanase in combination either with fungal exo-1,3-β-glucanase or β-glucosidase, liberated large amounts of glucose and other reducing groups. The results are discussed in relation to fungal cell wall structure and the role of host and fungal glycosidases in degrading the cell wall of fungal pathogens during infection.