Weanling pigs have reduced secretion of HCl in the stomach needed for appropriate protein digestion. Therefore, acidifiers are sometimes used in weaning diets as alternatives to antibiotic growth promoters because these products may create a favorable environment in the stomach for proper pepsin activity. However, the presence of limestone and monocalcium phosphate (MCP) in phase 1 diets, which have a high buffer capacity, may contribute to the inability for pigs to secrete enough HCl in the stomach, and lowering the inclusion level of these ingredients in starter diets may be beneficial to young pigs. Therefore, the objective of this experiment was to test the hypothesis that reducing the amount of limestone and MCP in diets for weanling pigs, by lowering the concentration of dietary Ca and P and(or) by including microbial phytase in the diet, will reduce stomach pH and fecal score and therefore improve growth performance of pigs.