Nephrogenesis in the human being proceeds until the 35th week of gestation. The anatomic immaturity of the kidneys in preterm neonates concurs with a functional immaturity on glomerular as well as on tubular level. The studies in this thesis are performed in order to analyse the effect of extrarenal influences on renal function in the developing kidney. Studies are in part performed in newborn rabbits before the end of nephrogenesis, and in part in preterm human neonates