Fluorometric determination of pseudocholinesterase activity in postmortem blood samples. A fluorometric assay using 3-(p-hydroxyphenyl) propionic acid (HPPA) was conducted to determine the activity of pseudocholinesterase (ChE) [Enzyme Commission (EC) No. 3.1.1.8] in postmortem blood samples so as to test for organophosphate poisoning. By the enzymatic reaction of ChE, its substrate, benzoylcholine, produces choline, which is oxidized by choline oxidase to generate hydrogen peroxide. HPPA is oxidized by hydrogen peroxide and peroxidase to become the fluorogenic dimer whose concentration is measured fluorometrically at an excitation emission wavelength of 320 nm and an elimination emission wavelength of 404 nm. The selectivity and sensitivity of the present method were found to be superior to those of conventional pH and spectrophotometric methods. 