The reaction pattern of the polygalacturonase from Helix pomatia juice has been studied. Hydrolysis of pectic acid occurs in a random manner. Oligogalacturonic acids are hydrolyzed in a sequential process, starting from the non-reducing end. This behavior is different from that of other endopolygalacturonases, which split these latter substrates both randomly and in a stepwise way from the reducing end.