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A model food chain was established to investigate the influence of grazing by flagellates on bacteria degrading toluene in batch culture. The rate of toluene consumed by a Pseudomonas sp. strain PS+ (max. 0.37 fmol cell(-1) h(-1)) was significantly higher in the presence of the bacterivorous flagellate Heteromita globosa (max. 1.38 fmol cell(-1) h(-1)). A maximum increase of up to 7.5 times was observed in the rate of toluene consumed by these bacteria during exponential growth of this flagellate. Carbon conversion efficiency (CCE) of bacteria to flagellate biomass was estimated to be 33.4% based on measured biovolumes and published values for carbon contents. However, the CCE for toluene-derived carbon was lower (max. 4.9%) when calculations were based on incorporation of [ring-U-(14)C]toluene into biomass of flagellates grazing on labelled bacteria. The findings suggest a potential role for flagellates in bioremediation processes.