Excessive phosphorus (P) output in the manure is a concern because it can leach into groundwater and/or may limit manure application onto certain lands. The addition of phytase enzyme to the diet of weanling pigs decreased total and water-soluble P output in the manure. This effects was reduced when dietary calcium was high relative to P (Ca:P ratios above 1.7:1). Phytase had only modest effects on performance.