BACKGROUND: Although a significant number of studies were done on focal segmental glomerulosclerosis(FSGS), its pathogenesis has not been sufficiently established yet. Recent studies suggested certain types of circulating factor(s) played an important role in development and recurrence after renal transplantation of FSGS by modifying the glomerular permeability of albumin. The purpose of this study performed on animals and through molecular-biological experiments is to certify the role of circulating factor (s), which cause proteinuria, by manipulating plasma of a FSGS patient who showed massive of proteinuria and wide effacement of glomerular epithelial foot processes in histologic examination after renal transplantation. also, whose massive proteinuria decreased significantly after plasma exchange. METHODS: The patient's plasma prior to(plasma A) or post to(plasma B) plasma exchange were injected into tail veins of two groups of male Sprague-Dawley rats, six in each. The ratio of 24 hour urine protein and urine creatinine(Uprt/Ucr) was calculated for each case. The 2D gel electrophoresis was performed in plasma A and plasma B. The pattern of 2D gel electrophoresis of plasma A was compared to those of plasma B and healthy human serum. RESULTS: Compared to control group, there was no significant differences in 24-hour Uprt/Ucr afer injecting 1, 2, 3, 5 mL of plasma A(p>0.05). There was no significant difference in 24-hour Uprt/Ucr between the injecting groups of plasma A and plasma B(p>0.05). We were not able to observe any new protein which did not appear in plasma B or healthy human serum in 2D gel electrophoresis. CONCLUSION: These results suggest that the proteinuria developed in a few hours after renal transplantation and is related to wide effacement of glomerular epithelial foot processes, and that it may be induced by a certain factor which is eliminated by the plasma exchange or restrained by the immunosuppressive agents. However, we were not able to find certain circulating factor(s) which rapidly changes albumin permeability in the patient's plasma with FSGS.