Chitin, chitosan and peptidoglycan induced chitinase (EC 3.2.1.14) activity in Parthenocissus quinquefolia cells cultured in vitro, while cellulose did not. The real inducers seemed to be oligomers released from the large size polymers by hydrolytic enzymes secreted into the medium during the cell growth and division. This effect was mimicked by the addition to the medium of a partially purified Parthenocissus chitinase/lysozyme (EC 3.2.1.17), which was also able to hydrolyse chitosan. Oligomers of chitin and of chitosan induced the activity to the same level and with the same time course, while peptidoglycan oligomers induced less activity. Oligomers also induced β‐1,3‐glucanase (EC 3.2.1.6) activities. The changes with time of both activities and the relative effects of the three kinds of polymers suggested that the induction of both enzymes involves a common element early in the signal pathway.