Deafness in dalmatian dogs in known to be congenital. It has been reported that the condition is manifested in structural defects of the sensitive lamina of the organ of Corti. In a study of deaf puppies, examined as they became available, this was found to be in doubt. Moreover, a characteristic gross reduction of area was found in the structure of the acoustic cortex in affected puppies. Extension of the morphometric studies further showed that the acoustic pathways were generally attenuated in keeping with the changes in the cortex. Consideration is given to the probability that the condition develops centrally rather than peripherally. Thus instead of the central components failing to develop because of lack of evocative stimulus from the end organ it is envisaged that the peripheral organ regresses because of incomplete innervation by central outgrowth.