Two four week trials and three 5 weeks trials were conducted to determine the effectd of adding Yucca extract or anhydrous calcium chloride to nursery diets on the growth performance of nursery pigs and aerial ammonia concentration. The pigs were weaned between 13-15 days of age and had an initial bodyweight of 3-6 kg. In each trial, pigs were allotted three diets 1) control-containing 23% crude protein, 2) control plus 125ppm of Yucca extract 3) control plus 1.95% anhydrous calcium chloride. Growth performance was recorded weekly. Aerial ammonia concentration was measured using aspiration detector tubes. Manure samples were collected twice during the experimental period to determine ammonia and N concentrations and pH. Plasma urea concentration was determined in blood samples collected from the pigs at the end of each trial. Data were analyzed using split-plot and latin square designs for the preliminary and makor studies. Feed intake was similar among pigs fed all three diets. There was no difference in ADG and ADFI between pigs fed the control diet and pigs fed the Yucca extract diet. In all trials pigs fed the calcium chl;oride deit had lower ADG in grower-finisher than pigs fed all other diets. In the preliminary study, aerial ammonia tended to be greater in rooms with pigs fed Yucca extract> In the major study aerial ammonia increased weekly in all rooms. In the fourth week ammonia concentrations were higher in rooms where pigs were fed the control diet than in rooms where the other two diets were fed. Dietary treatment had no effect on plama urea concentration manure ammonia and N concentrations and manure pH. Although aerial ammonia concentration was relatively low the additionof Yucca and anhydrous calcium chloride to the diet of nursery pigs reduced ammoni concentrations in the nursery rooms.