Purity >95%. L-NIL is a relatively selective inhibitor of iNOS. It exhibits IC50 values of 0.4-3.3 μM for iNOS as opposed to 8-38 and 17-92 μM for eNOS and nNOS, respectively. L-NIL effectively inhibits iNOS both in vitro and in vivo . L-NIL has been used to demonstrate a critical role for iNOS in the immune response to infection by the protozoan L. major .