The fine structure of fibroblasts and Schwann cells in the iris stroma was studied by electron microscopy. The basement membrane of Schwann cells was well stained with ruthenium red, although it was discontinuous. In contrast, the iris fibroblasts were almost devoid of the basement membrane. Of special interest is that the density of cytoplasm differed between the fibroblasts and Schwann cells in the iris stroma. The cytoplasm of iris fibroblasts showed high density, whereas that of Schwann cells, low density. The thin processes of the characteristic fibroblasts often surrounded naked axons containing numerous synaptic vesicles. It was demonstrated that ruthenium red staining is more useful than other stainings in the morphological distinction between the fibroblasts and Schwann cells in the iris stroma.