At 18 to 19 days of incubation the heads of chick embryos were removed from the egg. Three groups of subjects were formed by injecting a silicone ruber adhesive into either the left, right, or both ear canals. A fourth nontreated group acted as controls. Embryos were returned to the incubator and allowed to hatch normally. Between 24 and 72 hours the chick neonates were anesthesized, the ear plug(s) removed, and the animals were mounted in a head holder. A sound‐probe tube system was sealed over the left and right tympanic ring. The neostriatum was exposed to reveal the optic tectum and a concentric electrode was inserted into the right Mesencephalicus Latoralis pars Dorsalis (MLD). Evoked‐response thresholds for test frequencies between 0.125 and 5.0 kHz and the relation between stimulus SPL and evoked‐response amplitude at 0.25, 0.5, 1.0, and 2.5 kHz were measured in every subject for left‐ and right‐ear stimulation. The results indicate no differences in threshold sensitivity between all sound‐deprived and control animals. However, the relation between SPL and evoked‐response amplitude at 0.25 and 0.5 kHz was significantly different between deprived and control subjects. The results indicate that an early conductive hearing loss results in abnormal auditory development which is probably located in the nervous system. [Work supported by NSF.]