 Two new tracers for GFR measurement are here offered for validation: Gd-DOTA and Calcium-EDTA. Gd-DOTA is a macrocyclic paramagnetic contrast product, which can be measured using an ELISA type immunoassay. Although being widely used in radiology with higher doses than those that will be used for GFR measurement in the multi-GFR study, Gd-DOTA has never been involved in systemic nephrogenic fibrosis cases ProFinest study. Calcium-EDTA has been used for many years for the chelation of heavy metals. Recently, a colorimetric assay for Calcium-EDTA measurement has been developed. Gd-DOTA and Calcium-EDTA clearance for GFR measurement will be compared to inuline clearance in healthy volunteers 25 for each new tracer and CKD patients 150 for each new tracer. 