During the study of inhibition of nitric oxide production (in vitro) with inhibitors of nitric oxide synthase, it became apparent that frequently nitric oxide was also produced without the involvement of the enzyme nitric oxide synthase (NOS). For this reason, we have decided to also focus on non-enzymatic production of nitric oxide. In fact, we have found that some of the commonly used NOS inhibitors have dual functions. While inhibiting NOS activity, it is also enhancing non-enzymatic NO production. This study is important, especially when NOS inhibitors used clinically to suppress NO production is being compromised.