In order to further our basic understanding of the effects of lidocaine hydrochloride in the inner ear, cochlear potentials and blood flow (CBF) were assessed after intravenous (i.v.), anterior inferior cerebellar artery (AICA), and local round window (RW) lidocaine administrations in guinea pigs and rats. Lidocaine RW applications produced a dose dependent decrease in compound action potentials (CAP) and cochlear microphonics (CM). The sensitivity changes were more pronounced at high frequencies. These findings suggest that lidocaine has specific pharmacological action in the inner ear other than simple anesthesia of the auditory nerve. The basal turn endocochlear potentials (EP) were not altered by topical lidocaine, implicating altered organ of Corti function following local application of lidocaine. RW applications of lidocaine had no effect on CBF or systemic blood pressure (BP). I.v. infusions caused substantial reductions in BP. In the case of systemic infusions the percent changes in CBF were equal to and accountable by the BP changes. The microinfusions (50 mg/ml, 100 nl/min) through AICA produced a 30%, long lasting increase in CBF. However, neither systemic lidocaine nor AICA infusions had an effect on CAP or CM. These findings indicate that systemically given lidocaine may not cross the blood-cochlear barrier and that the cochlear electrophysiological effects due to lidocaine when given locally are partly mediated by direct influence on cochlear hair cell function; they also suggest that lidocaine-induced interference with active ion transport in the lateral wall or an influence on CBF are not contributing factors.