Electrical potentials in response to sounds were recorded from the inner ear of 3 spp. of turtles of the family Emydidae. The recording electrode was given 3 locations on the cranial wall of the otic capsule, in the dorsal part of the perilymph space close to the posterior semicircular canal and utricle, and on the round window membrane. These locations are increasingly efficacious in the order named, but the second is the most practical for systematic; measurements. The turtle''s ear is highly sensitive, and rather uniformly so, for faint tones in the region up to 500 cycles. For higher tones, however, the sensitivity falls off with great rapidity, and beyond 3000 cycles a measurable potential can be obtained only at the risk of injury by overstimulation. The sensitivity for low tones is of the same order as that determined by similar methods in the cat, and in one of the species studied (the wood turtle, Clemmys, insculpta) is nearly equal to that of the cat for higher tones, where this animal has its maximum sensitivity. For intense stimuli the turtle''s ear makes a poorer showing. It has only a limited dynamic range; its potential is a linear function of sound pressure only at low levels, and as the intensity is raised overloading quickly set in. Measured from 0.1 microvolt, the lowest level at which reliable observations were made, the turtle''s range of linearity is about 20 db and its maximum range of response is about 40 db, whereas the cat''s range of linearity for low tones is about 66 db and its maximum range is 80 db. It seems resonable to suppose that the turtle has relatively poor loudness discrimination for any but the faintest sounds. The general correspondence of the inner-ear potentials of the turtle to the cochlear potentials of birds and mammals evidently represents a basic similarity in the nature and operation of the auditory sense cells.