The scanning electron microscope (SEM) was used to investigate morphological changes to the chinchilla cochlea following chronic extracochlear electrical stimulation. Silver ball electrodes were placed on round window membranes and various types and levels of electrical pulsatile stimulation was given. Positive or negative square wave pulse (with DC offset) stimulation caused severe damage to the organ of Corti. In the most severely damaged area, most outer hair cells were missing and degenerative changes to pillar cells were observed. Some damage to the inner hair cells was also evident. These changes were limited to the basal turn. Some damage to stereocilia of first row outer hair cells was seen when symmetrical, biphasic, charge balanced pulses were used.