Various abalones and sea-hares from California and Brittany (France) were surveyed for their cellulase, fucanase, protease and alginate lyase activities. The crude digestive juices contained significant amounts of cellulase, fucanase and alginate lyase but very low levels of protease. The alginate lyases from both the sea hare Aplysia depilans and the abalone Haliotis tuberculata preferentially degraded polymannuronate sequences. Haliotis tuberculata alginate lyases were partially purified by cation exchange chromatography. For the purpose of protoplast preparation from brown algae, the purification procedure was scaled up to produce about 30 000 units of alginate lyase activity, with a 100-fold purification coefficient, in one run. This fraction did not retain cellulase, fucanase or proteolytic activities.