The degradation of eight unlabeled highly condensed polycyclic aromatic hydrocarbons (PAH) and the mineralization of three C-14-labeled PAH by the white-rot fungus Pleurotus sp. Florida was investigated. Three concentrations containing 50, 250 or 1250 mu g each unlabeled PAH/5 g straw were added to sterile sea sand. Selected treatments were added subsequently with C-14-labeled pyrene, benzo[a]anthracene or benzo[a]pyrene. The PAH-loaded sea sand was then mixed into straw substrate and incubated, The disappearance of the unlabeled four-to six-ring PAH : pyrene, benzo[a]anthracene, chrysene, benzo[b]fluoranthene, benzo[k]fluoranthene, benzo[a]pyrene, dibenzo[a,h]anthracene and benzo[ghi]perylene, was determined by high-performance liquid chromatography. After 15 weeks of incubation, the recoveries were less than 25% for initial amounts of 50 mu g (controls above 85%). The recoveries of unlabeled PAH increased in the inoculated samples with increasing concentrations applied. No correlation could be determined between the number of condensed rings of the PAH and the recoveries of added PAH. Pleurotus sp. Florida mineralized 53% [C-14]pyrene, 25% [C-14]benzo[a]anthracene and 39% [C-14]benzo[a]pyrene to CO2 in the presence of eight unlabeled PAH (50 mu g applied) within 15 weeks. During the course of cultivation, Pleurotus sp. Florida degraded more than 40% of the wheat straw substrate. Variation of the initial concentration of PAH did not influence the extent of degradation of the organic matter.