The newborn rabbit was used as an experimental model for studying renal changes during normocapnic hypoxemia. Renal extraction of p-aminohippuric acid (PAH), as assessed in 15 normoxemic and 8 hypoxemic rabbits amounted to 54.6 ± 3.7 and 45.7 ± 4.6%, respectively (NS). Changes in glomerular filtration rate (GFR), and renal blood flow (RBF) as assessed by inulin and PAH clearances, respectively, were determined during norm oxemia and subsequent hypoxemia in 8 additional anesthetized and mechanically ventilated newborn rabbits. Normocapnic hypoxemia (PaO₂ = 38.6 ± 2.1 mm Hg) induced a significant fall in GFR from 2.10 ± 0.21 to 1.51 ± 0.18ml/kg/min (p < 0.01), in filtration fraction (p < 0.01) and U/P inulin ratio (p < 0.01). RBF, renal vascular resistance and urine flow rate did not change significantly. In comparison with other immature animal species the newborn rabbit appears a valuable and inexpensive model for the study of acute hypoxemia-induced renal changes.