Bisphenol A was oxidized to monoquinone and bisquinone derivatives by Fremy's salt, a radical oxidant, though salcomine and alkali did not catalyze the oxidation by molecular oxygen. Bisphenol A, bisphenol B, and 3,4'-(1-methylethylidene)bisphenol were converted to their monoquinone derivatives in the presence of tyrosinase at 25 degrees C at pH 6.5, but not to the bisquinone derivatives under these conditions.