Milk production was measured and phosphorus (P) excretion in feces was estimated in dairy cows fed three amounts of P. A basal diet was formulated to contain 0.31% P (DM basis). Sodium monophosphate replaced corn in the basal diet to give two additional diets containing 0.40 and 0.49% P. The diets were fed to eight, nine, and nine multiparous Holsteins from the beginning to the end of lactation. Milk yields for the 308-d lactation were 10,790, 11,226, and 11,134 kg for the three treatments, respectively. The lowest milk yield resulted from decreased milk production during late lactation with the 0.31% P group. Reproductive performance of the cows was not related to dietary P content. Fecal P concentration, determined in wk 2, 4, 6, 8, 23, and 40 of lactation, increased as dietary P intake was increased. Cows fed the lowest P diet conserved P by minimizing P excretion in feces and urine, whereas cows in the other two treatments excreted more P through these routes. A reduction in dietary P from 0.49 to 0.40% reduced fecal P excretion by 23%. Apparent P digestibilities of less than 40% are indicative of surplus dietary P. Feeding 0.40% P appeared sufficient to maintain P balance and the level of milk production achieved in this experiment. An example is given which illustrates the relationship between dietary and fecal P.