Studies on the natural history of the norepinephrine (NE) model of acute renal failure (ARF) in the dog. Group I (n = 6) was infused with NE into the renal artery (0.75 µg/kg/min × 80 min) and glomerular filtration rate (GFR) determined sequentially. 21 days post-NE infusion (I) the GFR of the I kidneys (20 ± (SE) 5 ml/min) remained less (p < 0.001) than the pre-I control value (44 ± 2.9). Group II (n = 7) was treated in an identical fashion except that a contralateral nephrectomy (CN) was done on day 7 and the animals were prepared for micropuncture on day 16. In the animals with residual nephron function at CN, the GFR increased (p < 0.02) from 26 ± 6.4 ml/min on day 7 to 38 ± 6.6 ml/min on day 14. Considerable interanimal heterogeneity of single nephron GFR (SNGFR) was demonstrated and morphologic studies revealed a very patchy lesion. Therefore, the model is reversible, heterogeneity of SNGFR is present, and the residual functioning nephrons have the capacity to undergo an increase in GFR after CN.