SOUZA, N.H. Rumen metabolism and the mineral balance in water buffaloes with different levels of the phosphorus intake. 2004. 53f. Tese (Doutorado) – Faculdade de Zootecnia e Engenharia de Alimentos, Universidade de Sao Paulo, Pirassununga, 2004. Four mature buffaloes fitted with rumen cannulas were used to study the effects of different levels of the phosphorus intake on the ruminal metabolism and the digestion in the diets. Ammonia concentration, pH, fluid and solid outflow rates, rumen volume; concentration of mineral in the ruminal content; digestibility and estimate of faecal output of minerals were determined. The animals were designed in Latin Square experiment (4x4) with each period of 28 d of duration. Treatments were applied four rations with different levels of P intake (8, 12, 15 e 18 grams). The proportion forage for concentrate was 85:15 with only using fresh chopped sugar cane. No differences were observed among the treatments in the rumen parameters evaluated and digestibility. Increasing in phosphorus intake resulted in simple linear regression equation Y = 0.03 + 0.610 * X, where P output daily (g (kg bodyweight)) was used as the dependent variable (Y) and P intake daily (g / kg) was used as the independent variable (X).