The visual acuity of a cichlid fish, Astronotus ocellatus Agassiz, was measured by means of a conditioned visual discrimination response. The average minimum separable visual angle was 5.3’, as measured in 16 fish with at least one normal eye; this corresponded closely to the fineness of grain of the retinal receptor mosaic. In 12 fish, acuity of one experimental eye was measured after the optic nerve had been transected and allowed to regenerate. The value for postregenerative acuity was then compared with a previous value for acuity of one normal eye in one and the same fish, in each case. Restoration of acuity by regenerative processes averaged 78.4%. This high figure shows that formation of functional, specific synaptic contacts probably does not occur on a chance basis.