The steady-state kinetics, product identification, stoichiometries, and solvent isotope effects of yeast alcohol dehydrogenase catalyzed reduction of p-nitroso-N,N-dimethylaniline (NDMA) by NADH, are reported. NDMA is enzymatically reduced to p-hydroxylamine-N,N-dimethylaniline, which is further enzymatically dehydrated to corresponding quinonediimine cation (QDI+). QDI+ undergoes nonenzymatic transformations. QDI+ is rapidly reduced by NADH to p-amino-N,N-dimethylaniline (ADMA). Also, QDI+ is readily dismutated with ADMA to form N,N-dimethyl-p-phenylenediamine radicals; radicals are stable under steady-state conditions, below pH 7.5. A complete kinetic mechanism for above reactions has been proposed.