Atmospheric ammonia is known to enhance surface and soil water acidification and eutrophication, increase the nitrogen (N) load on semi-distant vegetation, and contribute to atmospheric turbidity and radiative forcing by enhancing fine aerosol formation.  The greatest contribution to atmospheric ammonia (NH₃) comes from agricultural sources.  There is a paucity of data regarding ammonia volatilization from grazing beef and dairy operations in the southeastern United States.  This study quantified NH₃ volatilization from dairy and beef cattle defecation and urination on pasture under field conditions in Auburn, Alabama on a Pacolet sandy loam soil.  Treatments consisting of beef feces, dairy feces, dairy urine and an untreated control were arranged in a completely randomized design with six replicates on swards measuring 1 m².  The experiment was conducted during four seasons from June 2003 to April 2004.  Simulation of fresh fecal and urine deposition was facilitated by applying a known amount of fresh feces or urine onto a known area of grass sward.  Ammonia volatilization was measured periodically up to 14 days after treatment application using an inverted chamber method.  Cumulative NH₃ volatilization from beef feces and dairy feces was not significantly different from the control, which had no NH₃ volatilization during the study.  Dairy urine was the only significant source of NH₃ volatilization.  Total cumulative NH₃ volatilization from dairy urine differed among seasons, with total NH₃-N loss ranging from 1.8 % in January to 20.7 % in June.  The highest rate of NH₃ volatilization generally occured within 24 hours after application.  Cumulative NH₃-N volatilization from dairy urine is described by the equation %NH₃-N loss = N_max(1-e^-ct)ⁱ.  This study suggests that NH₃ volatilization from cattle urine on pasture is significant and variable, while that from cattle feces is negligible.