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Renal function was measured in an Australian parrot, the galah (Cacatua roseicapilla), which is distributed across the most arid regions of the continent. Renal function was assessed by the "constant infusion" technique in hydrated galahs, and in both hydrated and dehydrated birds by means of osmotic minipumps. The glomerular filtration rate (GFR) of the galah is similar to calculated values for a bird of its size. However, effective renal plasma flow tended to be low and therefore filtration fraction was high. Water deprivation for a period of 5 days caused a decrease in body weight and an increase in plasma osmolality and haematocrit. The GFR declined steadily such that weight-specific GFR on the fifth day of water deprivation was 68% of control values. The water deprivation produced a 2.6-fold elevation of plasma arginine vasotocin (AVT) levels, with an overall sensitivity of release of AVT of 0.16 +/- 0.02 pg.ml-1 per mOsm.kg-1. The galah possesses renal mechanisms which enable it to conserve significant amounts of water during times of water stress.