H₂S is produced by enzymes and has various physiological roles including neuromodulation, vascular tone regulation, cytoprotection against oxidative stress. We previously demonstrated that H₂S relaxes vascular smooth muscle in synergy with NO. In the process of the study about the effect of H₂S on transient receptor potential (TRP) channels, we found that H₂S_n activates TRP ankyrine 1 (TRPA1) channels much more potently than does H₂S and that 3-mercaptopyruvate sulfurtransferase (3MST) produces H₂S₂ and H₂S₃. The chemical interaction of H₂S with nitric oxide (NO) has been reported to generate several products including nitroxyl (HNO), nitrosopersulfide (HSSNO) and H₂S_n. The effect of H₂S_n on TRPA1 channels is suppressed by reduction and by cyanide, while that of HNO is resistant to reduction and that of HSSNO to cyanide. Based on these observations we concluded that H₂S_n are chemical entities generated by the interaction of H₂S with NO. I will focus on the production of H₂S_n and a potential mechanism of the synergistic effect of H₂S and NO.