OBJECTIVE This study is aimed at determining if tibial nerve stimulation (TNS) can modulate both bladder underactivity and overactivity. METHODS In α-chloralose anesthetized cats, tripolar cuff electrodes were implanted on both tibial nerves and TNS threshold (T) for inducing toe twitching was determined for each nerve. Normal bladder activity was elicited by slow intravesical infusion of saline; while bladder overactivity was induced by infusion of 0.25% acetic acid to irritate the bladder. Bladder underactivity was induced during saline infusion by repeated application (2-6 times) of 30-min TNS (5 Hz, 4-8T, 0.2 msec) to the left tibial nerve, while TNS (1 Hz, 4T, 0.2 msec) was applied to the right tibial nerve to reverse the bladder underactivity. RESULTS Prolonged 5-Hz TNS induced bladder underactivity by significantly increasing bladder capacity to 173.8% ± 10.4% of control and reducing the contraction amplitude to 40.1% ± 15.3% of control, while 1 Hz TNS normalized the contraction amplitude and significantly reduced the bladder capacity to 130%-140% of control. TNS at 1 Hz in normal bladders did not change contraction amplitude and only slightly changed the capacity, but in both normal and underactive bladders significantly increased contraction duration. The effects of 1 Hz TNS did not persist following stimulation. Under isovolumetric conditions when the bladder was underactive, TNS (0.5-3 Hz; 1-4T) induced large amplitude and sustained bladder contractions. In overactive bladders, TNS during cystometry inhibited bladder overactivity at 5 Hz but not at 1 Hz. CONCLUSIONS This study indicates that TNS at different frequencies might be used to treat bladder underactivity and overactivity.