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1 The e ects of two sigma (s) binding site ligands, (+)-pentazocine and 1,3-di-o-tolylguanidine (DTG), on bladder functions were examined in rats. 2 Cystometry using urethane-anaesthetized rats showed that (+)-pentazocine (1 ± 5 mg kg 71 , i.v.) and DTG (1 ± 5 mg kg 71 , i.v.) prolonged micturition intervals, indicating increased bladder capacity and raised the threshold pressure.3 The e ects of (+)-pentazocine (2 mg kg 71 , i.v.) on micturition were not in¯uenced by naloxone (0.5 mg kg 71 , i.v.), which antagonized similar e ects of morphine (2 mg kg 71 , i.v.). 4 When administered intracerebroventricularly (i.c.v.), DTG (1 mg) and (+)-pentazocine (30 mg) prolonged micturition intervals with increased threshold pressure on the cystometrogram. 5 In isolated bladder detrusor strips of rats, (+)-pentazocine (3 mM) and DTG (1 mM) did not a ect contractile responses to electrical ®eld stimulation. A higher concentration of DTG (3 mM) slightly suppressed the response induced by 30 Hz stimulation.6 The e ects of (+)-pentazocine and DTG on micturition were abolished by pre-treatment with pertussis toxin (PTX, 1 mg, i.c.v.). 7 These results indicate that typical s ligands, such as (+)-pentazocine and DTG, increase bladder capacity in anaesthetized rats. Moreover, the mechanism by which s ligands change the urinary storage properties in rats may involve pathways in which the function of Gi/o proteins is necessary.