H2S is an important gasotransmitter with a vasorelaxant property. The modulation of endogenous H2S generation from different tissues and the functional consequence of this modulation are not clear. In the present study, the production of H2S from vascular tissues as well as the liver and ileum of rats was measured. The H2S production rate was significantly greater in rat liver than rat vascular tissues. H2S production in rat aortae, ileum, and liver tissues was upregulated by sodium nitroprusside in a cGMP-dependent fashion. Amino-oxyacetate (AOA) (1 mM) abolished H2S production in liver tissues and partially inhibited H2S production in the ileum, while D,L-propargylglycine (PPG) at a similar concentration only slightly inhibited H2S production in liver. Intraperitoneal injection PPG, but not AOA, significantly suppressed H2S production in liver, aorta, and ileum tissues. The systolic blood pressure of rats was significantly increased 2-3 weeks after i.p. injection of PPG. It is concluded that the endogenous production of H2S could be modulated by NO. AOA and PPG have different capacities in regulating the endogenous production of H2S in different types of tissues.