This article is a report on a symposium sponsored by the American Society for Pharmacology and Experimental Therapeutics and held at the Experimental Biology 01 meeting in Orlando, FL. The presentations addressed the mechanisms of inhibition and regulation of cytochrome P450 and flavin monooxygenase enzymes by nitric oxide. They also highlighted the consequences of these effects on metabolism of drugs and volatile amines as well as on important physiological parameters, such as control of blood pressure, renal ion transport, and steroidogenesis. This is achieved via regulation of P450-dependent prostacyclin, hydroxyeicosatetraenoic acid, and epoxyeicosatrienoic acid formation. Conversely, the mechanisms and relative importance of nitric oxide synthases and P450 enzymes in NO production from endogenous and synthetic substrates were also addressed.