Structural differentiation of Kranz anatomy has been investigated in leaf cross sections of two C-4 Poaceae: Digitaria sanguinalis and Setaria viridis. The study mainly focused on cellular and interfacial features of bundle sheath (BS) and mesophyll (MS) cells of the C-4 structure. Prominent BS, spaced by only two MS cells apart, were surrounded concentrically by a layer of MS cells. BS cells of S. viridis had centrifugally arranged reltively large chloroplasts containing much starch, but the chloroplasts had agrana to rudimentary grana. Structural and size dimorphisms, when starch was present, were detected between BS and MS chloroplasts. Loosely arranged MS cells had peripherally displaced smaller chloroplasts containing little to none starch. BS chloroplasts of D. sanguinalis were similar to those of S. viridis, but had very little starch and well-developed peripheral reticulum (PR) was easily recognized in MS chloroplasts of S. viridis. Virtually no PR was developed in BS chloroplasts examined. BS cells contained more mitochondria and microbodies, but no structural dimorphism was niticed. The electron-dense suberized lamella were often observed between BS and MS cells, especially in the primary wall of BS cells. It was most frequently found at the BS and MS cell interfaces and terminated in radial walls of theadjacent BS cells. Prominent pits with plasmodesmata (pd) were seen in the walls of both cells. There also were numerous pd in outer tangential walls of the BS cells. The number of pd ranged from 20 to 60. The pd trasversed a segment of cell wall much thinner than the adjacent wall. The current cellular data have been compared to the ultrastructural features known in leaves of other C-4 plants, especially NADP-ME species.