Four experiments were conducted to evaluate the efficacy and safety of a microbial phytase (Novo SP938) in weanling and grower pigs, and starter turkeys fed corn-soybean meal based diets. Pig and turkey BW and pen feed consumption were recorded weekly. Fecal and excreta samples were collected for determination of Ca and P digestibility. At the end of all experiments animals were slaughtered, and 10th ribs or right foot for pigs, and both middle toes for turkeys were removed for bone analysis. In pigs performance, bone measurements, and digestibilities of P and Ca increased as levels of phytase increased. Concentration of P and Ca in the feces decreased as dietary phytase increased. In turkeys, BW gain and toe ash increased as nonphytate P or phytase increased, when added to a low-P diet. Concentrations of P and Ca decreased as phytase was added to the diet. Based on nonlinear or linear equations, the average P equivalency of 500 U phytase/kg feed was .64 and .67 g of inorganic P for pigs and turkeys, respectively. There were no adverse effects of feeding 10,000 U phytase/kg feed in pigs and turkeys. Supplementation with Novo SP938 phytase was effective in improving performance, bone mineralization, P and Ca utilization, and decreasing P and Ca concentrations in the feces of pigs and excreta of young turkeys fed low-P diets, with no health effects, even at very high supplementation rates.