Abstract: The invention is a process for preparing tetraalkyl-substituted biphenol which comprises reacting a 2,4- or 2,6-dialkyl substituted phenol in which the alkyl groups contain 1 to 6 carbon atoms with a peroxidase enzyme in the presence of a peroxide in an aqueous medium to yield a tetraalkyl-substituted biphenol by oxidative coupling of the 2,4- or 2,6-dialkyl substituted phenol, or yielding a tetra-alkyl substituted quinone, and reducing the quinone to obtain a tetraalkyl-substituted biphenol. The invention further includes a process for preparing a tetraaryl-substituted biphenol in which the aryl groups contain 6 to 10 carbon atoms which comprises racting a 2,4 or 2,6 diarylphenol with a peroxidase enzyme to yield a tetraaryl-substituted biphenol. A process for reducing a tetraalkyl-substituted quinone to corresponding tetraalkyl-substituted biphenol which comprises reducing the quinone with a phenol in an aqueous medium at a temperature of about 60° to 120° C. is also included.