In an attempt to study further the stellate cell and its functions, the ultrastructure of this cell type in the neurointermediate lobe of the bullfrog, Rana catesbeiana, was examined in both organ and dissociated-cell culture. The cytoplasmic activity of stellate cells from neurointermediate lobes incubated 3 1/2 or 5 1/2 h was greater than that of those in vivo. Mitochondria and bundles of cytoplasmic filaments were numerous, in addition to prominent, well-developed Golgi complexes with associated vesicles. The most striking ultrastructural feature was the presence of phagocytic vacuoles that contain cellular debris. The stellate cells were seen to form cytoplasmic processes that phagocytosed this extracellular debris identifiable as belonging to the secretory cells of the pars intermedia. The stellate cells from the dissociated-cell preparations were also seen to contain debris within phagocytic vacuoles. In those neurointermediate lobes transplanted for 3 1/2 to 4 days into the anterior chamber of the eye, the stellate cells demonstrated similar phagocytic ability, but the phagocytic vacuoles contained material that seemed to be at a later stage of degradation. In all three of these conditions, the stellate cells were not seen to release this cellular debris nor were they seen to undergo cell division. These glial-like stellate cells of the pars intermedia acted as macrophages in all three of these experiments. There is now, therefore, a need to determine under what conditions, if any, these stellate cells function in vivo as macrophages.