SUMMARYThe marine deuteromyceteZalerion maritimumwas grown in a simulated marine environment containing the chlorinated cyclodiene pesticides aldrin and dieldrin, with and without glucose. Fungal response was measured in terms of dry wt and cell-nitrogen increase. Pesticide fate was observed by gas-liquid and thin-layer chromatography (TLC) of culture-fraction extracts after growth with unlabeled compounds and by scintillation and radioautographic TLC assays of culture-fraction extracts after growth with“C-labeled compounds. Growth of the fungus was stimulated by up to 250μg/ml of the pesticides which appeared to be partially degraded to hydrophobic and hydrophilic metabolites. Aldrin did not appear to degrade via dieldrin and the close structural relationship did not always elicit comparable behavior. Dieldrin, more possibly than aldrin, may have been cometabolized with glucose. The fungus appeared to absorb about 2000-fold more pesticide than remained in growth media which indicates bioconcentration and possible negative effects on the ocean food chain.