L-N6-(1-iminoethyl)lysine 5-tetrazole amide (SC-51 or L-NIL-TA) is rapidly converted in vivo to the active metabolite L-N6-(1-iminoethyl)lysine (L-NIL). L-NIL is a relatively selective inhibitor of nitric-oxide synthase type 2 (NOS2). Unlike L-NIL, L-NIL-TA has minimal inhibitory activity in vitro on human NOS2. However, it is rapidly converted in vivo to L-NIL and produces dose-dependent inhibition of iNOS in acute and chronic models of inflammation in the rodent with efficacy comparable to L-NIL. L-NIL-TA produces marked inhibition of exhaled breath NO in normal and asthmatic subjects without producing the side effects observed following the systemic administration of non-selective NOS inhibitors, and thus provides support for the potential use of iNOS inhibitors to treat a range of inflammatory clinical disorders.