The lignin peroxidase enzyme system of the white-rot fungus, Phanerochaete chrysosporium, was assayed for its capacity to degrade two recalcitrant aliphatic ether compounds, high-molecular-mass polyethylene glycol (PEG 20000) and methyl tert-butyl ether. Ligninolytic cultures of Phanerochaete chrysosporium were spiked with each ether compound and incubated in reaction vessels. Separate incubations were conducted in which the ether compounds worn present as sole carbon source. Other parameters, such as varying the methyl tert-butyl ether concentration and veratryl alcohol additions were tested. No significant degradation of either compound was observed under any of the conditions tested. Implications nf these results are discussed with respect to the oxidative limitations of the lignin peroxidase enzyme system and structural features of substrate molecules that mag be requisite for oxidation by this system.