BACKGROUND: Phosphodiesterase type 5 inhibitors (PDE5-Is) are effective in the treatment of lower urinary tract symptom (LUTS), although their mechanism of action is still unclear. PDE5-Is cause bladder detrusor relaxation, and this effect is partially independent of nitric oxide. Hydrogen sulfide (H(2)S) is a newly discovered transmitter with myorelaxant properties. It is predominantly formed from L-cysteine by cystathionine-β-synthase (CBS) and cystathionine-γ-lyase (CSE). OBJECTIVE: To evaluate whether the L-cysteine/H(2)S pathway contributes to the relaxing effect of sildenafil on the human detrusor dome. DESIGN, SETTING, AND PARTICIPANTS: Samples of bladders obtained from men undergoing open prostatectomy for benign prostatic hyperplasia (BPH) were used. The presence of CBS and CSE enzymes was assessed by western blot. H(2)S production was measured by a colorimetric assay in basal and stimulated conditions with L-cysteine and in response to sildenafil (1, 3, 10, and 30μM), 8-bromo-cyclic guanosine monophosphate (8-bromo-cGMP; 100μM) or dibutyryl-cyclic adenosine monophosphate (dibutyryl-cAMP; 100μM). A curve concentration effect of sodium hydrosulfide (NaHS), H(2)S donor (0.1μM to 10mM), L-cysteine (0.1μM to 10mM), and sildenafil (0.1-10μM) was performed on precontracted detrusor dome strips. To investigate H(2)S signaling in a sildenafil effect, CBS and CSE inhibitors were used. OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS: Analysis of variance was used, followed by the Bonferroni post hoc test. RESULTS AND LIMITATIONS: CBS and CSE are present in the human bladder dome and efficiently convert L-cysteine into H(2)S. Both NaHS and L-cysteine relaxed human strips. Sildenafil caused (1) a relaxation of bladder dome strips and (2) a concentration-dependent increase in H(2)S production. Both effects were significantly reduced by CBS and CSE inhibitors. Similar to sildenafil, both 8-bromo-cGMP and dibutyryl-cAMP caused an increase in H(2)S production. CONCLUSIONS: The sildenafil relaxant effect on the human bladder involves the H(2)S signaling pathway. This effect may account in part for the efficacy of PDE5-Is in LUTS. A better definition of the pathophysiologic role of the H(2)S pathway in the human bladder may open new therapeutic approaches.