Concentrations of ammonia (NH3) and hydrogen sulfide (H2S) in ambient air were semicontinuously measured at a 50,000-head cattle feedyard in Texas panhandle in three seasons: fall 2002 (10 days), winter 2003 (14 days), and spring 2003 (15 days). Sampling was conducted at 1.5 m above the ground at one location each season at the western fence line of cattle pens. Gas concentrations were measured using continuous analyzers housed in an onsite instrument shelter. Measured concentrations were upwind or downwind of the feedyard pens depending on the wind direction. Wind directions, wind velocity, and air temperature were measured to correlate them with measured concentrations. Higher concentrations were measured when the sampling port was located downwind from the feedyard. The average NH3 concentrations for the fall, winter, and spring based on hourly-averages were 429 ppb, 475 ppb, and 712 ppb, respectively. The highest hourly average of 5,270 ppb for NH3 was measured in the spring 2003, followed by the 2,890 ppb in the fall 2002. The average H2S concentrations for the fall, winter, and spring based on hourly-averages were 7.73 ppb, 0.73 ppb, and 2.45 ppb, respectively. The highest hourly average of 34.9 ppb for H2S was measured in the spring 2003, followed by the 29.6 ppb in the fall 2002. The NH3 and H2S concentrations had a characteristic daily pattern with two local maximums in the early afternoon and early evening hours. The lowest concentrations were always measured during the night. The experimental setup worked well and proved itself to be reliable in widely different weather conditions and operational for unattended and automated measurements.