Diethylamine (DEA) and nitric oxide (NO) form a stable 1:1 complex (DEA/NO) which can be oxidized to N-nitrosodiethylamine (NDEA). Spectroscopic data for the complex are consistent with the ionic structure originally proposed by Drago & Paulik (1960). Attempts to confirm this structure by X-ray crystallography are continuing. Oxidation of DEA/NO to NDEA appears to be effected by an acid-catalysed dissociation to DEA and NO, followed by autoxidation of NO to an N-nitrosating higher oxide of nitrogen.