enzymes such as cytochromes P450, guanylate cyclase, cy­ clooxygenase, and mitochondrial cytochrome oxidase continues to emerge as a key area in NO- research. In addition, it has become clear that the expression of NOS isoforms and NO- release from cells is subject to regulation by sexual steroids and that, in tum, NO- has the potential to regulate steroid biosynthesis via inhibition of cytochromes P450 involved in steroidogenesis. These recent observations on interactions between the NO-/NOS and cytochrome P450/sexual steroid pathways have important implica­ tions for understanding fundamental mechanisms involved in endocri­ nological processes. They are also likely to lead to novel insights and novel therapeutic approaches for the management of pathophysiologi­ cal conditions associated with alterations in sexual steroid hormones.