The histological localization of fibrinolytic activity in the developing eye of rat was studied by means of the histochemical fibrin slide technique. The observation that fibrinolytic activity is related to small vessels provided a means of following the developing vascularization of the eye. The hyaloid vascular system was found fully developed, together with the tunica vasculosa lentis, at the 18th day of intrauterine life. Involution of these vessels begins between the third and the seventh day after birth. The retinal vessels begin to develop between the 16th and the 18th day of intrauterine life. The choroid acquires fibrinolytically active vessels in the second week of life. At this time also the ciliary body becomes vascularized. The patterns of appearance and disappearance of sites of fibrinolytic activity observed during the development of the eye are related to the functional morphology of the involved tissues.