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Atmospheric emissions of ammonia, as well as other gases and particulates are a growing concern of livestock producers, the general public and regulators. The concentration and form (rapidly degradable in the rumen vs. slowly degradable in the rumen) of protein in beef cattle diets may affect urinary and fecal excretion of nitrogen and thus may affect ammonia emissions from beef cattle feedyards. To determine the effects of dietary protein concentration and degradability on potential ammonia emissions, 54 steers were randomly assigned to 9 dietary treatments in a 3 x 3 factorial arrangement of treatments. Treatments consisted of three dietary crude protein concentrations (11.5, 13, and 14.5%) and three supplemental urea:cottonseed meal ratios (100:0, 50:50, and 0:100 of supplemental N). Steers were confined to tie stalls and feces and urine excreted were collected and frozen. One percent of daily urine and feces excretion were mixed and added to polyethylene chambers containing 1,550 g of soil. Chambers were sealed and ammonia emissions were trapped in an acid solution for seven days using a vacuum system. Results suggest that as the protein concentration in the diet increases from 11.5 to 13%, potential daily ammonia emissions increased 60 to 225 %, due primarily to increased urinary N excretion. As days on feed increased, in vitro ammonia emissions also increased. Potential daily ammonia emissions must be balanced with possible effects on animal performance to determine optimal protein concentrations and forms.