Evidence is presented that linamarase is a cell-wall bound enzyme. It can be extracted using high concentrations of sodium chloride. The activity is maximal at pH 5.5. Bound and solubilized enzyme exhibit a Km value of about 8 mM on linamarin. Linamarase also hydrolyses the artificial substrate 4-methyl umbelliferyl-/?-D-glucoside. Besides linamarase, at least three other /i-glucosidases are present, exhibiting activity towards the artificial substrate. These enzymes exhibit no or hardly any activity towards linamarin and differ in isoelectric point from linamarase. The presence of linamarase is regulated by the gene Li, the other /J-glucosidases being independent of Li, In natural populations, plants with and without linamarase activity are observed. The percentage of plants exhibiting linamarase activity, is dependent on the altitude of the locality of the population.