Purpose : It has been reported that endothelin-1 can be associated with the development of cyclosporine A nephrotoxicity. Levels of endothelin-1 was assayed to determine the effect of cyclosporine A on the plasma and urine levels of this peptide. Method : Nine patients who were less than 15 years of age and were also diagnosed as steroid dependent minimal change nephrotic syndrome were included in this study. Assay of endothelin-1 was done before and 3 months after cyclosporine A treatment. The mean age of the patients was 8.3 ±4.6 years. Result : There was no significant differences in the plasma levels of endothelin-1 before and after 3 months of cyclosporine A treatment (3.22±0.39 pg/mL vs. 3.84±1.52 pg/mL, P=0.64). Also there was no changes in the urine levels of endothelin-1 (21.8 ± 5.8 pg/mL vs. 20.3 ±3.1 pg/mL, P=0.30). Conclusion : No significant changes of endothelin-1 levels were found with 3 months of cyclosporine A treatment. Further studies with longer durations will help clarifying the effect.