The limited capacity for weanling pigs to secret HCl in the stomach may be exacerbated by inclusion of ingredients with high acid binding capacity such as limestone and monocalcium phosphate. As a consequence, reducing the amount of these 2 ingredients in diets for weanling pigs may contribute to a stable low pH for proper pepsin activity and increased action of microbial phytase. Inclusion of high doses of phytase that results in increased phytate degradation and increased release of Ca, P, and inositol may also be beneficial to newly weaned pigs. Therefore, an experiment was conducted to test the hypothesis that lowering dietary Ca and P reduces gastric pH and diarrhea of weanling pigs, but microbial phytase may overcome negative effects of low Ca and P on growth performance and bone ash.