Cunninghamella elegans degraded tributyltin (TBT) at 20 mg l(-1) when grown in Sabouraud medium. Above this concentration, growth was inhibited. After 7 d 70% TBT (added at 10 mg l(-1)) was converted to less toxic derivatives: dibutyltin and monobutyltin. TBT metabolism was totally blocked by cytochrome P-450 inhibitors, metyrapone and proadifen. Only in medium with 1-aminobenzotriazole, was dibutyltin (0.42 mg l(-1)) found after 7 d of culturing. It is postulated that the significant resistance of C. elegans to TBT is associated with the capacity of the fungus to metabolise TBT.