Deficiency of cyclooxygenase-2 (COX-2) activity in the early postnatal time course causes impairment of kidney development leading to kidney insufficiency. We hypothesize that impaired NaCl reabsorption during the first days of life is a substantial cause for nephrogenic defects observed in COX-2-/- mice and that salt supplementation corrects these defects. Daily injections of 0.8 mg/g/d NaCl for the first 10 days after birth ameliorated impaired kidney development in COX-2-/- pups resulting in an increase in glomerular size and reduction of immature superficial glomeruli. However, impaired renal subcortical growth was not corrected. Increasing renal tubular flow by volume load or injections of KCl did not relieve the renal histomorphological damage. Administration of torsemide and spironolacton also affected nephrogenesis resulting in diminished glomeruli and cortical thinning. Treatment of COX-2-/- pups with NaCl/DOCA caused a stronger mitigation of glomerular size and also induced a slight but significant growth of cortical tissue mass. After birth renal mRNA expression of NHE3, NKCC2, ROMK, NCCT, ENaC, and Na+/K+-ATPase increased relative to day P2 in wild type mice. However, in COX-2-/- mice a significantly lower expression was observed for NCCT, while DOCA/NaCl treatment significantly increased NHE3 and ROMK expression. Regarding long-term effects of postnatal NaCl/DOCA injections improved kidney function with normalization of pathologically enhanced creatinine and urea plasma levels and albumin excretion was observed. In summary we present evidence that a salt supplementation during the COX-2 dependent time frame of nephrogenesis partly reverses renal morphological defects in COX-2-/- mice and improves kidney function.