Resin acids, major components in the lipophilic extractives of many coniferous pulpwood species, are known to display high acute toxicity against aquatic organisms and bacteria in wastewater treatment systems. In the present study we examined the ability of several white-rot fungal strains to degrade different resin acids. Results obtained in solid-state fermentation studies with Scots pine wood as well as in liquid culture experiments with resin model compounds show the high effectiveness of fungal treatment to reduce the content and/or the acute inhibitory effect (Microtox assay) displayed by toxic pitch constituents. Several (novel) metabolites of the fungal transformation of dehydroabietic acid were isolated and identified. These included polar intermediates, mainly hydroxylated-, dihydroxylated and hydroxyl-oxodehydroabietic acids.