1. The visual acuity of the peripheral retina was measured using both sinusoidal gratings viewed in the usual way and interference fringes formed on the retina directly.2. It is shown that optical aberrations cause a reduction in peripheral visual acuity for eccentricities of less than 5 degrees . However, the hypothesis that optical defects are a major cause of the well-known decrease in acuity with eccentricity is rejected.3. The fringe acuities at various retinal positions are compared with Osterberg's counts of the distribution of cones. It is shown that at eccentricities of less than 2 degrees , resolution approaches the theoretical limits for a mosaic of receptors.