1. Epidermal growth factor (EGF) has recently been shown to stimulate both polydipsia and polyuria and the aim of this study was to determine which was the primary response. Ewes received a continuous intravenous saline infusion (100 ml day‐1) for 12 days (days 1‐12) and EGF at doses of 0 (n = 6) or 10 micrograms h‐1 (n = 6) over days 5‐8. The supply of water was ad libitum during days 1‐4 and 9‐12, but was fixed at the pretreatment mean of days 1‐4 for each ewe during days 5‐8. 2. During the period of fixed water intake, the EGF‐treated ewes experienced mild dehydration with elevated plasma osmolality, sodium, renin and arginine vasopressin (AVP) concentrations and slightly reduced plasma atrial natriuretic peptide (ANP) concentrations. 3. When the supply of water returned to ad libitum, the EGF‐treated ewes increased their water intake by 105% (5.25 +/‐ 0.28 vs. 2.55 +/‐ 0.19 l day‐1) and subsequently fluid balance was restored; plasma electrolyte and hormone responses also returned to normal. 4. This experiment demonstrates that EGF infused at a dose rate of 10 micrograms h‐1 I.V. into sheep has a direct renal diuretic effect.