Chlorophyliase (Chlase) is widely distributed in higher and lower plants and differs in activity. It occurs in various organs. In some plants the enzyme is synthesized in cytoplasm, in others in chloroplasts. Various Chlase forms are known. Participation, in the chlorophyll (Chl) degrading systém belongs to the main fimctions of Chlase. Moreover, it may catalyse Chl biosynthesis and takés part in photosynthesis. The Chlase activity is stimulated by radiant energy, sublethal freezing, heavy metals (Hg, Zn, Cu), Fe and Mn deficiency, and mosaic virus infection. The effect of water content on Chlase activity depends on individual plant organs. Osmotic and saline- osmotic stress decreases Chlase activity, but NaCl can stimulate the activity. The influence of plant age depends on plant genus. Some growth regulators (ethylene, heteroauxin, abscisic acid) increase Chlase activity, others (kinetin, dicarboxylic monoesters, gibberellic acid, gibbérellin A3) inhibit it. The mechanisms of Chlase action are also reviewed.