Background: Nephrotic Syndrome (NS) is a clinical state characterized by massive proteinuria, hypoalbuminemia and eventual edema formation. Although the mechanisms underlying this phenomenon are not yet fully clarified, it is well accepted that nephrin and podocin are involved in the development of proteinuria. The effects of early treatment with various anti-proteinuric therapies on proteinuria, and glomerular staining of nephrin and podocin in rats with experimental NS have not been previously studied. Methods: Proteinuria and glomerular nephrin and podocin immunofluorescence were examined in rat kidneys with adriamycin-induced NS and the effects of anti-proteinuric drug therapies during 5 weeks with enalapril, losartan, alone or in combination, omapatrilat, and mycophenolate mofetil on these parameters were assessed. Results: Injection of adriamycin caused a significant increase in daily (from 21.8±1.4 to 983.1±45.8 mg/day, P<0.01) and cumulative protein excretion (from negligible values to 22490±931 mg (P<0.001), during 5 weeks. Early treatment with enalapril significantly decreased the daily (641.7±82.4 mg/day, P<0.0023) and cumulative proteinuria (15727±2204 mg (P<0.001). A similar effect, although to a lesser extent, was obtained after omapatrilat treatment: cumulative proteinuria was reduced to 18706±1042 mg, P<0.001. In contrast, losartan treatment did not significantly influence the cumulative proteinuria which remained comparable (20351 ± 1360 mg, P>0.05) to that observed in untreated NS rats. Unexpectedly, when losartan was given in combination with enalapril it abolished the beneficial effects of the latter. Pretreatment with mycophenolate mofetil exerted a moderate anti-proteinuric effect, which appeared only during last week of the experimental treatment. Nephrotic rats exhibited severe disruption of slit diaphragm structure as seen by rapid and profound loss of nephrin and podocin. Beneficial effects of enalapril, omapatrilat, and mycophenolate mofetil paralleled the preservation of nephrin, as determined immunohistochemically, and enabled prediction of significant anti-proteinuric responses. Enalapril alone or in combination with losartan resulted in significant preservation of podocin. Conclusions: Pretreatment with enalapril, and to a lesser extent, omapatrilat, is superior to losartan in reducing proteinuria in NS rats. Combination of ACE-I with ARBs does not provide any advantageous antiproteinuric therapy in these animals. Nephrin loss is an indication of proteinuria in NS and the antiproteinuric effects of ACE-I, VPI, and mycophenolate mofetil attenuate this reduction. Not all the drugs which restore podocin reduce urinary protein in NS.