Control of non-point sources of nitrogen to prevent surface water eutrophication and groundwater contamination is a major challenge faced by water quality managers. Critical non-point sources of nitrogen include animal wastes, on-site wastewater treatment systems, atmospheric deposition, combined sewer overflows and urban and agricultural runoff. A number of best management practices (BMPs) have been used for control of non-point pollutants, including grassed swales, infiltration and detention basins, media filters, and wetland systems. Little information is available; however, on the design, performance and optimization of stormwater BMPs for total nitrogen removal. This research investigated a denitrifying bioretention system for total nitrogen removal. In the denitrifying bioretention system, runoff is conveyed to a ponding area and gradually infiltrates through a nitrifying sand filter. The nitrified stormwater travels through a submerged denitrification zone, which is supplied with an electron donor, where nitrate is reduced to nitrogen gas by anoxic heterotrophic or autotrophic bacteria. Two pilot scale reactors were tested, which utilized either wood chips or elemental sulfur as electron donors for denitrification. Influent and effluent BOD5, COD, pH, alkalinity, total N, ammonium, nitrate, nitrite, sulfate, phosphate and solids concentrations were measured over time during selected storm events. Tests performed under controlled laboratory conditions with simulated runoff resulted in 90% total N removal after system acclimation. Results of field tests under varying operating conditions with runoff from a dairy farm in Putnam, Connecticut will be presented at the conference.