The single nephron glomerular filtration rate (SNGFR) was determined in superficial (S) and juxtamedullary (JM) nephrons of 10 anesthetized rabbits by the14C ferrocyanide infusion technique. The length of the proximal tubules and the volume of the glomeruli were also determined for the same nephrons. SNGFR was higher in JM than in S: 28.6±3.4 versus 22.6±3.0 nl/min,P<0.001. In JM nephrons, glomeruli were larger than in S: 1.3±0.1 versus 0.9±0.1 nl,P<0.001, whereas there was no difference between proximal tubule length in either category (S, 8.7±0.3 and JM, 8.9±0.5 mm). In 6 out of 8 animals, SNGFR was significantly correlated to glomerular volume. Lack of correlation was observed between SNGFR and length of proximal tubule in all animals but one. These results show that the rabbit, as well as small rodents and the dog, has a higher SNGFR in juxtamedullary than superficial glomeruli. Although this functional difference is not related to the length of the proximal tubule in each individual animal, the ratio between the mean SNGFR value and the mean length of the proximal tubule in superficial rabbit nephrons is similar to the ratio found in other species.