Six healthy adult cats were fed a basal minced beef meat and rice diet with varying amounts or combinations of acidifying and alkalizing additives (ammonium chloride, calcium and sodium carbonate). The base excess in the food (mmol/kg dry matter) was calculated (data on food compounds in g/kg dry matter) as follows: base excess = 49.9*Ca + 82.3*Mg + 43.5*Na + 25.6*K - 64.6*P - 13.4*Met-16.6*Cystine -28.2*Cl. It amounted to between +305 and -1079 mmol/kg dry matter. Urine and blood pH as well as balance of minerals and water were determined in the cats. The mean urine pH ranged between 6.1 and 7.8. There was a highly significant correlation between the base excess in the food and the mean urine pH. The regression line was linear down to a base excess in the diet of about -400 to -500 mmol/kg dry matter and a pH in the urine of 6.2. The postprandial increase of urine pH was suppressed either by large amounts of ammonium chloride (> 780 mmol/kg dry matter) alone or in combination with calcium carbonate, but not in combination with sodium carbonate. The relationship between the decrease of the blood pH and the amount of ammonium chloride added to the diet was more marked than the relationship between blood pH and base excess in the food. In order to avoid health risks by long term application of acidifying diets it is recommended to formulate struvite diets with low base excess in such a way, that they contain as few alkalizing compounds as possible, which must be neutralized by acidifiers.