Bacterial secondary production and rates of bacterivory were determined from samples collected from mesotrophic Lake Arlington. Bacterial production and losses were determined by comparing the growth of natural bacterial assemblages in the presence of predators (unfiltered samples) to growth in the absence of predators (water filtered through 1.0 mum porosity filters). Growth rates of heterotrophic nanoflagellates (HNF) were estimated from growth in the absence of predators (water filtered through 5.0 mum porosity filters). Bacterial growth rates ranged between 0.002 and 0.069 h-1, and averaged 0.026 h-1. HNF grew at rates ranging between 0.003 and 0.107 h-1 and averaged 0.028 h-1. Grazing rates ranged between 0.002 and 0.043 h-1, and averaged 0.018 h-1. The annual average rate of bacterial biomass synthesis was 3.2 mug C l-1 h-1 and approximately 69% of this production was grazed. Temporal changes in growth and grazing rates suggest a tightly coupled predator-prey linkage in this lake.