Cells on the ependymal surface of hypothalamic third ventricle of hamsters exhibit surface, ultrastructural, and phagocytic features of macrophages. The object of this investigation was to identify functions that a resident phagocytic system of the ventricles of the brain may have normally. We found that supraependymal macrophages in two- to three-week-old hamsters were associated with intact and degenerating intraventricular neuronal processes, ependymal cytoplasmic blebs, and degenerating intraventricular cells. These macrophages frequently contained cellular debris within phagosomal vacuoles. In the vicinity of neuronal ganglion on the floor of the third ventricle, there were numerous structures identified as growth cones, with organelles in varying stages of alteration and degeneration. Supraependymal macrophages apparently remove cellular debris resulting from ependymal metabolic processes and from cellular and neuritic degeneration. Such activity may be part of a normal process of remodeling, involving cell growth, renewal, or cell death within the third ventricle of developing animals.