A beta-fucosidase located in the latex serum of Lactuca sativa has been isolated and purified to homogeneity. This enzyme greatly differs from the other fucosidases already known in that it is strictly specific for the fucosyl residue and for the anomeric beta carbon. It is the first time that such an enzyme is shown to exist. The enzyme is a monomer and its molecular mass is close to 37 kDa. Its sedimentation constant is equal to 2.8 S. It is very stable at pH 5.5 in citrate/phosphate buffer but extensive denaturation occurs up to pH 7.5. Kinetic studies have shown that two ionization steps probably control the rate of the enzymatic hydrolysis. No precise information could be obtained about the possible in vivo role of this beta-fucosidase. However, the pure enzyme can release fucose from the cell walls obtained from hypocotyls of L. sativa. This result may be taken as evidence for the presence of beta-fucosidic links in these walls so that the enzyme could be involved in the differentiation of articulated laticifers.