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Renal clearance experiments were conducted on feral chickens descended from birds collected from a coral island off the coast of Queensland, Australia. Following a control period when 0.13 M NaCl was used as a vehicle for the renal function markers, a salt load was imposed by infusion of 1 M NaCl. The hypertonic NaCl infusion resulted in increases in glomerular filtration rate (GFR), effective renal blood flow (ERBF), and urine flow rate (V), whereas filtration fraction decreased. Haematocrit was reduced and plasma osmolality, sodium, chloride and potassium concentrations increased. Plasma arginine vasotocin (P(AVT)) levels increased from 31.4 perpendicular-to 2.3 pg. ml-1 during the control infusion to 56.0 +/- 1.7 pg. ml-1 following a salt load of 12 mmol NaCl. kg-1. The sensitivity of release of AVT was 0.69 +/- 0.11 pg. ml-1 per mosmol.kg-1. The concentrations of Na and Cl in urine increased, whereas urine osmolality and potassium concentration decreased. The expansion of the extra-cellular fluid volume induced by the salt loading would tend to suppress the release of AVT, whereas the osmotic stimulus would-provide a stimulus for the release of AVT. In this study, GFR, HRBF and ERPF increased at the same time as P(AVT) increased.