A factorial experiment was conducted to determine the factors controlling denitrification in the northern Chihuahuan Desert. Specifically, we measured the response of denitrification to additions of water, C, N, and C + N.... When denitrification rates were averaged across vegetation zones and patch types (between or under vegetation), the following treatment effects were significantly different: water + NO3 + C >>> water + NO3 = water >> water + C > control. These results indicate that denitrification at this site is limited by the availability of water. (The study was conducted along the LTER-I Control Transect.)