Mechanisms of generation of reactive oxygen forms (ROF) by external surfaces of marine sponges Sycon sp. and actiniae Aiptasia pulchella were studied. Activities of enzymes participating in production (myeloperoxidase, xanthine oxidase) and inactivation (superoxide dismutase, catalase) of ROF were measured. Effects of action of different chemical substances on ROF production by studied objects were studied. Inhibitors and stimulators of the enzymes participating in ROF production, stimulators of phagocytosis, alimentary attractants, and changes of water ion composition were used. The obtained data allow suggesting the ROF production by sponges Sycon sp. and actiniae Aiptasia pulchella to represent a Ca2+-, protein kinase C-, and potential-dependent process provided by activity of enzymes similar to NADPH-oxidase of the higher animal and human plasmalemma. In sponges this process is associated with phagocytosis, while in actiniae—with activity of nettling cells.