The white rot basidiomycete Phanerochaete ch~Tsosporium metabolized 4-ethoxy-3-methoxyphenylglycerol-fi-guaiacyl ether (V) in low nitrogen, stationary cultures under which conditions the ligninolytic enzyme system is expressed. 4-Ethoxy-3-methoxyphenylglycerol XIII, guaicol and 4-ethoxy-3-methoxybenzyl alcohol (II) were isolated as metabolic products. Exogenously added XIII was rapidly converted to 4-ethoxy-3-methoxybenzyl alcohol indicating that it is an intermediate in the metabolism ofV. P. chrysosporium also metabolized 1-(4'-ethoxy-3'-methoxyphenyl)-2-(2"-methoxyphenoxy)-3-hydroxypropane VI. The degradation pathway for this dimer also included initial 13-ether cleavage and c~-hydroxylation of the diol product 1-(4'-ethoxy-3'-methoxyphenyl) 2,3 dihydroxypropane (XI) to yield the triol XIII which was cleaved at the c~,/~ bond to yield 4-ethoxy-3-methoxybenzyl alcohol. Finally P. chrysosporium also cleaved the dimer 1-(4'-ethoxy-Y-methoxy- phenyl)-2-(2"-methoxyphenoxy)-1-hydr oxypropane (VIII) at the fi-ether linkage yielding 1-(4'-ethoxy-3'-methoxyphenyl) 1,2 dihydroxypropane (IX) which was subsequently cleaved at the c~, 1~ bond to yield II. All of the results indicate that oxidative 13-ether cleavage is an important initial reaction in the metabolism of/~-aryl ether lignin subsructure dimeric compounds. Metabolities were identified after comparison with chemically synthesized standards by gas liquid chromatography-mass spectrometry.