We probe endogenous NO production in WKY rats by trapping NO with iron-dithiocarbamate complexes. The aim was to detect non-stimulated NO production in small organs like kidneys of juvenile rats. The yields of mononitrosyl Fe-dithiocarbamate complexes are small and difficult to quantify in the presence of strong contaminating signals from Cu2+-DETC complexes. We evaluate four methods to improve the detection of mononitrosyl Fe-dithiocarbamate adducts: progressive microwave saturation, tissue perfusion, spectral subtraction, and finally, reduction of the tissue with sodium dithionite. While the first three were only moderately useful, reduction was very helpful for quantification of the mononitrosyl Fe-dithiocarbamate yield. The increase in sensitivity allows the detection of non-stimulated NO release in small organs of juvenile rats.