Cyclosporine induced nephrotoxicity in renal transplant recipients. Clinical significance of fractional excretion of sodium, potassium, and magnesium. Evaluation of fractional excretion of sodium(Na), potassium(K), and magnesium(Mg) as indicators for cause of early renal dysfunction after renal transplantation. A cross-sectional comparative study on 59 live related renal allograft recipients from the 1st day of transplantation, and compared with 30 healthy controls. Serum creatinine was recorded from 1st day and %FE of Na, K and Mg were noted on 5th and 10th day. Spot CsA levels on 1st day and AUC were also recorded. The mean serum creatinine in renal transplant recipients at first day was 3.77+1.35 Vs .76+.16 in healthy control (p=0.000), on 5th day it was 1.76+1.3 Vs .76+.16 (p=0.000) and on 10th day it was 1.73+1.25 Vs .76+.16 (p=0.000) . %FENa in recipients on 5th day was 3.2+5.9 Vs .55+.34 in healthy control (p=0.000) and on 10th day 2.2+2.5 Vs .55+.34 (p=0.000). %FEK in recipients on 5th day was 10.69+12 Vs 2.84+1.05 (p=0.172) in healthy controls and on 10th day 11.37+14.5 Vs 2.84+1.05 (p=.165). %FEMg in recipients on 5th day was 11.4+9.5 Vs 6.02+2.34 in healthy control and on 10th day 11.2+8.1 Vs 6.02+2.34. On comparison of patients of CsA-toxicity and patients with renal graft rejection only %FEMg have significant difference at 5th day (p=0.018) and at 10th day (p=0.039).Spot Cs-A at first day and AUC was not significant. In Conclusion, CsA therapy increase urinary excretion of Mg which is not dependent on dose of CsA. There is significant increase in %FEMg in patients having CsA-toxicity. Therefore %FEMg can be used as a chemical marker for differentiation of renal graft dysfunction in early post-transplant period.