Abstract(#br)Hydrogen sulfide (H 2 S) is the endogenously produced gasotransmitter involved in the regulation of nervous system, cardiovascular functions, inflammatory response, gastrointestinal system and renal function. Together with nitric oxide and carbon monoxide, H 2 S belongs to a family of gasotransmitters. H 2 S is synthesized from l -cysteine and/or l -homocysteine by cystathionine β-synthase, cystathionine γ-lyase and cysteine aminotransferase together with 3-mercaptopyruvate sulfurtransferase. Significant progress has been made in recent years in our understanding of H 2 S biochemistry, signaling mechanisms and physiological role. H 2 S-mediated signaling may be accounted for not only by the intact compound but also by its oxidized form, polysulfides. The most important... signaling mechanisms include reaction with protein thiol groups to form persulfides (protein S-sulfhydration), reaction with nitric oxide and related species such as nitrosothiols to form thionitrous acid (HSNO), nitrosopersulfide (SSNO − ) and nitroxyl (HNO), as well as reaction with hemoproteins. H 2 S is enzymatically oxidized in mitochondria to thiosulfate and sulfate by specific enzymes, sulfide:quinone oxidoreductase, persulfide dioxygenase, rhodanese and sulfite oxidase. H 2 S donors have therapeutic potential for diseases such as arterial and pulmonary hypertension, atherosclerosis, ischemia–reperfusion injury, heart failure, peptic ulcer disease, acute and chronic inflammatory diseases, Parkinson's and Alzheimer's disease and erectile dysfunction. The group of currently available H 2 S donors includes inorganic sulfide salts, synthetic organic slow-releasing H 2 S donors, H 2 S-releasing non-steroidal antiinflammatory drugs, cysteine analogs, nucleoside phosphorothioates and plant-derived polysulfides contained in garlic. H 2 S is also regulated by many currently used drugs but the mechanism of these effects and their clinical implications are only started to be understood.