Most lignin research has been on wood-rot fungi and not on other lignolytic organisms. Members of the genusAspergillus inhabit lignin-rich environments, and we have studied their relative lignin-degrading potential.Aspergillus fumigatus, A. japonicus, A. niger, andA. terreus were tested for their ability to metabolize14C-labeled aromatic compounds. The species tested decarboxylated, demethoxylated, and cleaved the rings of coumaric, ferulic, vanillic, veratric, and anisic acids. More than 90% of C-ring-labeled ferulic and vanillic acids disappeared from the medium in 96 h of cultivation. More than half of the above was respired, the rest was incorporated in unknown form into the mycelium. Mycelia were homogenized and about 3% of the initial label was found in TCA precipitate of the cell-free supernatant. Protocatechuic acid 3,4-dioxygenase (EC 1.13.11.3) and catechol 1,2-dioxygenase (EC 1.13.11.1) activities were detected in the mycelial extracts of theAspergillus spp.