Abstract
Phenols which markedly enhance chemiluminescence in the horseradish peroxidase catalysed oxidation of luminol by hydrogen peroxide show anomalously high reactivity (by factors of ∼102 compared with published Hammett correlations) in the reduction of the enzyme intermediates, Compound I and Compound II. The results support the hypothesis that efficient production of phenoxy radicals from phenols is a necessary criterion for chemiluminescence enhancer action.