Chronic kidney disease, i.e. a progressive and irreversible decline in glomerular filtration rate (GFR), is a major socio-economic, medical and scientific challenge. Correct and timely measurements of GFR in risk groups like patients with diabetes mellitus and hypertension seem therefore essential in order to prevent an epidemic increase in end stage renal failure and need for renal replacement therapy. Unfortunately, there are presently no satisfactory non-invasive methods to measure GFR. Plasma creatinine is far too insensitive and urinary clearance measurement of a GFR marker like inulin or creatinine is troublesome, time consuming and does not provide information of single kidney function. Isotop renography and SPECT suffers from low resolution and exposure of relatively large amount of radioactive materials. We have therefore developed new probes for molecular imaging of renal function using PET that is highly specific for filtering nephrons. Since the GFR-marker accumulates quantitatively and exclusively in filtering nephrons close to their parent glomeruli, the dose can be reduced by two orders of magnitudes as compared to conventional tracers used in nuclear medicine. Furthermore, potential side effects are minimized by utilizing endogenous substances already present in human body fluids. Proof of concept in 10 anaesthetized farm pigs with different unilateral perturbations of renal function will be presented and the potential clinical and scientific value of the new technology will be discussed.