Rates of potential denitrification were determined for anaerobic aquifer sediments collected at a site where groundwater NO3 concentrations ranged from 0.7 ??M to 8.6 mM. A significant relation (p = 0.046) was observed between denitrification rates and the in situ concentration of NO3, but NO3 concentration only accounted for approximately 34% (r2) of the variation in activity. The highly significant relation (p < 0.001; r2 = 0.80) between potential denitrification and sediment total organic content and the enhanced activity of sediments amended with glucose indicated that denitrification rates in this aquifer system were carbon limited. No significant relation was observed between denitrification and the in situ groundwater pH, but short-term variations in pH influenced both the magnitude and the end products of denitrification. ?? 1992 American Chemical Society.