Environmentally benign chemistry is an increasingly important topic both in the classroom and the laboratory. In this experiment, students synthesize divanillin from vanillin or diapocynin from apocynin, using horseradish peroxidase and hydrogen peroxide in water. The dimerized products form rapidly at ambient temperature and are isolated by filtration. The products are readily distinguished from starting materials by solubility, NMR spectroscopy, or melting point analysis. The experiment is adaptable to an organic chemistry course in the context of radical reactions of phenols, to a biochemistry course in the context of metalloenzymes, or to an advanced general chemistry course in the context of green chemistry. (Contains 2 schemes.)