A multicenter prospective study was done in four-university hospital to evaluate the efficacy and safety of cyclosporin A(CyA, Cipol-N(R)) in 64 patients with adult nephrotic syndrome mean age 34.8 years, male:female 2.4:1, duration of disease 38.0+/-40.9months, 31 patients with MCD, 33 patients with Non-MCD (8 FSGS, 14 MGN, 7 MPGN, 2 lupus nephritis, 1 HBsAg associated GN)]. The prior steroid responses of these patients were 17 steroid dependent, 9 frequent relapser, 4 steroid resistant and 1 other in MCD patients, and 5 steroid dependent, 5 frequent relapser, 22 steroid resistant and 1 other in Non-MCD patients. After a 2-week steroid (predni-solon 10mg/day or deflazacort 12mg/day) run-in period, CyA 5mg/kg/day and prednisolone 10mg/day (or deflazacort 12mg/day) were administered for up to 16 weeks. Of the 64 patients enrolled, ll patients were dropped out prematurely due to adverse events or protocol violation. Of the 53 patients who completed the study, 27 had MCD and 26 had Non- MCD. High response (CR and PR) rate of 68% (36/53) were obtained with CyA treatment in all patients. Although the response rate in MCD was significantly higher than that in Non-MCD (89 vs. 46%, p<0.05) and response rates were significantly different according to the previous steroid responses by univariate analysis, only previous steroid responses affected the response to CyA significantly by Logistic multiple regression analysis (p=0.03, RR 7.08); responses were 84% (27/32) in steroid dependent and frequent relapser patients, and 37% (7/19) in steroid resistant patients. 24-hr proteinuria significantly decreased after 2 weeks and serum albumin and cholesteroi increased significantly after 4 weeks of treatment compared to baseline level. The serum creatinine level was not changed during the study. No serious and unexpected side event was observed. In conclusion, cyclosporine therapy is a safe and effective mode of treatment in patients with ne-phrotic syndrome, especially in those who need prolonged administration of steroids with resulting in unavoidable steroid complications such as frequent relapser and steroid dependent type. The patients with steroid resistant type and contraidications of steroid administration such as DM, aseptic bone neerosis etc. can also be candidates for this treatment.