These experiments compared the cardiovascular effects and the alterations in orofacial blood flow resulting from hypotension induced with sodium nitroprusside and adenosine triphosphate infusions in 30 male rats. The authors found that sodium nitroprusside did not significantly change heart rate or cardiac output, while adenosine triphosphate caused a significant decrease in heart rate associated with a small increase in cardiac output. Both hypotensive agents produced similar profound decreases in total peripheral resistance. Blood flows to orofacial structures were qualitatively similar with both agents. Both adenosine triphosphate and sodium nitroprusside caused decreased flows to the maxilla and mandible. Sodium nitroprusside increased flows to masseter and suprahyoid muscles. Adenosine triphosphate caused increased flows to suprahyoid muscles but masseter muscle flows were not significantly changed. Tongue flows responded similarly to both agents, initially decreasing, then returning to normotensive levels. Finally, sodium nitroprusside-induced hypotension was associated with the development of tachyphylaxis in some animals, whereas no similar problem was observed with use of adenosine triphosphate. The demonstration of reduced blood flows to orofacial bony structures and the absence of resistance or tachyphylaxis during adenosine triphosphate-induced hypotension support its usefulness as a hypotensive agent during orthognathic and other surgery.