Conversion of urea in cattle urine to ammonia and its subsequent volatilization is thought to be the primary route for nitrogen emission in beef cattle feedlots. Nitrification under aerobic conditions represents an alternative, but poorly studied, route for nitrogen transformation in beef cattle feedlots. Soil samples were collected over a nine-month period from three sites (near the feed bunk, on the central mound, and at the down gradient end) in a beef cattle feedlot pen. Potential ammonia-oxidation activity measured in slurries varied by site and throughout the nine-month study with rates ranging from below detectable levels to 1.6 micromoles per hour per gram dry soil. The abundance of ammonia-oxidizing bacteria (AOB) also varied by site and time and ranged from below detection limit (10⁴) to 10⁸ AOB per gram dry soil. Nitrite-oxidizing bacteria (NOB) were typically 10-fold higher abundance compared to AOB. Correlations were generally weak among nitrification measures (potential activity and AOB/NOB abundance) and soil parameters (temperature, moisture content, percent organic matter, percent nitrogen, percent carbon, pH, and KCl-extractable ammonia and urea) or other microbiological factors (potential denitrifying activity, generic E. coli, and coliforms). Significant (P < 0.05) correlations were observed between nitrifying activity and denitrifying activity (r = 0.300) and AOB (r = 0.343) and between AOB and NOB (r = 0.306). This initial investigation indicates that potential nitrifying activity and the abundance of microorganisms responsible for that activity were quite high, especially compared to other soil systems. Thus, the fate of nitrogen in cattle feedlot soils may not be entirely determined by ammonia emission.