The prostaglandin H synthase (PGHS) reaction has been studied with syringaldazine as the electron donor. Kinetic parameters of the reaction agreed with those for commonly used electron donors. The sensitivity of the PGHS activity detection in the presence of syringaldazine increases 10 times. A sensitive spectrophotometric assay for polyunsaturated fatty acid (PUFA) detection using syringaldazine as a new electron donor has been proposed.