A study was conducted to define growth response of growing pigs to four levels of a unique, new, phytase enzyme and to determine how critical the Ca: available P ratio is to optimizing the utilization of the phytase enzyme in practical swine diets. Eighteen different diets were used (5 levels of phytase plus a positive control, at 3 different Ca:P ratios) for a 28-day growth and digestibility experiment. Neither performance (ADG, ADFI, feed conversion) nor P digestibility was affected by the Ca concentration in the diet. This result was unexpected and will require more research in the future. The improvement in ADG, ADFI and feed conversion with the inclusion of phytase reached a plateau at 250 U/kg inclusion rate. Phosphorus digestibility was improved in a linear manner with each incremental increase in phytase addition. The inclusion of 250 U/kg phytase in the diet reduced the amount of total phosphorus excreted in manure and increased phosphorus digestibility.