Dairy cows grazing a tropical grass pasture fertilized with 300 kg N/ha and with a 7-year history of phosphorus fertilizer at either 0 or 45 kg P/ha were given a P supplement in a 2 × 2 factorial experiment at Kairi Research Station, Queensland, Australia. Milk yield, fat-corrected milk yield, yields of milk fat, protein and lactose, and protein content of milk were increased (P<0·05) with P fertilizer. There was no response in milk yield or any component of milk to the provision of a P supplement. It is concluded that the milk response recorded in this experiment was due to P fertilizer leading to additional pasture on offer and increased pasture intake. The lack of response to additional P in the form of a supplement indicates that these pastures can supply adequate P for cows producing 20 kg/day even after 8 years without P fertilizer.