Abstract This study investigated the effects of dietary electrolyte balance (dEB=Na+K-Cl meq/kg DM) and acidifying Ca-salts on slurry pH and ammonia emission from slurry of growing-finishing pigs. Ninety gilts of about 40 kg BW were randomly allotted to 18 diets in five replicates. Two basal diets were used. Diet A had a high dEB (320 meq/kg DM) and diet B a low dEB (100 meq/kg DM). Each diet was supplemented with one of the four Ca-salts (CaCO 3, CaSO 4, Ca-benzoate or CaCl 2) to increase Ca content by 3 or 6 g per kg of diet. Faeces and urine were collected separately in metabolism cages and mixed as slurry. In a subsample of this slurry, pH and ammonia emissions were measured in a laboratory system. The low dEB diet produced urine and slurry with lower pH, and less ammonia was emitted from the slurry. Replacing dietary CaCO 3 by CaCl 2, CaSO 4 and Ca-benzoate reduced ammonia emission by 30, 33 and 54%, respectively. It is concluded that ammonia emission can be reduced by decreasing dEB level and adding CaSO 4 and CaCl 2 to the diet instead of CaCO 3. The most profound effect is achieved when CaCO 3 is replaced by Ca-benzoate.