The distribution of cytoplasmic filaments in lenses of five species was studied with the electron microscope. Two distinct patterns emerged. One pattern, in which filaments are grouped in characteristic bundles around the nucleus, in processes, and throughout the subcortical cytoplasm of epithelial cells, is typical of spherical, non-accommodating lenses of mice and rats. The second pattern is associated with anteriorly-flattened, accommodating lenses of infant human, squirrel and frog. In these, filaments are scattered in epithelial cells, but are accumulated on either side of the plasma membrane junction between epithelial cells and lens fibers. They are especially dense on the lens fiber side of the junction, and form a lattice associated with the lens fiber plasma membrane. The lattice is less extensive along the sides of lens fibers not in contact with epithelial cells. In spherical lenses the epithelial-fiber lattice is greatly reduced. Filaments in both types of lenses ranged in diameter between 5 and 11 nm. The filaments are thought to be a mixture of thin and intermediate filaments. It is hypothesized that the role of cytoplasmic filaments in lens, depending on the pattern present, is either to structurally support a spherical shape, or to provide a contractile force or elasticity to return the flattened anterior surface to the accommodated state in conjunction with the elasticity of the lens capsule.