In mice, an initial audiosensitizing sound (30 sec of a 95 db bell) induces seizure susceptibility to subsequent sound stimuli. Unilateral blockade of opposite ears during sensitization and testing reduced seizure incidence and severity in CF-1 mice, and prolonged latencies. Reduced total seizure incidence was best evidence of the unilateral component of the phenomenon since reduced severity was largely due to blockade of one ear during testing. The unilateral component increased with age and was striking only in animals audiosensitized at 21 days of age. Prolonged latencies were restored to control range by anesthesia during audiosensitization, but were unaffected by electroshock. Since the unilateral component of audiosensitization increases with age as susceptibility to sensitization is declining, both changes may be related to the development of inhibitory mechanisms.