Summary: This is the protocol for measuring Glomerular Filtration Rate (GFR) with minipump FITC-inulin clearance in mice. In brief, Alzet micro-osmotic pumps (minipumps, Model 1007D) are filled with 3% FITC-inulin solution. These pumps release FITC-inulin at a rate of 0.5 \u03bcl\/hr at least seven days. Mouse is temporarily anesthetized and then two mini-pumps are implanted in mouse peritoneal cavity through a tiny midline incision. After surgery, 24-hour urine is collected with metabolic cage and 100 \u03bcl of blood from saphenous vein is obtained at the same time. The concentrations of FITC-inulin in urine and blood samples are measured by flurometer and GFR is calculated by the concentration of FITC-inulin in 24-hour-urine and the concentration of FITC-inulin in plasma.