The degradation of two beta-5 lignin model dimers by Ceriporiopsis subvermispora was investigated. The beta-5 phenolic dimer was rapidly degraded by the fungus while the non-phenolic dimer remained untouched after 21 days of incubation under limited- and non-limited nitrogen conditions. Fungal degradation of phenolic compounds was a function of manganese concentration. When manganese was omitted from the medium the degradation of the phenolic compounds was much lower. Depletion of manganese was shown to strongly influence manganese peroxidase (MnP) production whereas laccase titer did not change. The beta-5 phenolic compound was degraded ill vitro by using a crude enzyme filtrate from C. subvermispora, Enzymatic degradation was enhanced both by Tween 80 and Tween 20. Vanillic acid was the predominant aromatic degradation product detected by GC/MS and LC/MS following fungal and enzymatic degradation. The addition of fully methylated beta-5 Compound in fungal liquid cultures almost completely inhibited MnP expression. Nevertheless, crude MnP activty from C. subvermispora was not affected in vitro by the fully methylated beta-5 compound indicating that in vivo some of the steps involved in its production were blocked. Preliminary results showed that crude MnP, in the presence of Tween 80, was able to oxidize the fully methylated beta-5 compound. In contrast, degradation in the presence of Tween 20 was very limited.