Epidemiologic studies suggest that higher serum phosphaturic hormone fibroblast growth factor 23 levels are associated with increase morbidity and mortality. The aim of the FGF23 Reduction Efficacy of a New Phosphate Binder in CKD Trial was to evaluate the effect of sevelamer carbonate on serum C-terminal fibroblast growth factor 23 levels in normophosphatemic patients with CKD stage 3b/4. Patients with CKD, eGFR between 45 and 15 ml/min per 1.73 m , fasting serum phosphate concentration >3.1 mg/dl, and serum C-terminal fibroblast growth factor 23 >80 relative units/ml were included in our double-blind, placebo-controlled, randomized multicenter study. All patients received 100,000 IU cholecalciferol at time of randomization. Participants received either placebo or sevelamer carbonate 4.8 g daily during a 12-week period. Biologic parameters, including serum C-terminal fibroblast growth factor 23, intact fibroblast growth factor 23, and -klotho, were evaluated at baseline and 12 weeks after inclusion. Of 96 screened patients, 78 (mean±SD age: 63±13 years old; 70% men; mean eGFR: 27±9 ml/min per 1.73 m ) met the inclusion criteria. At baseline, mean eGFR was 27±9 ml/min per 1.73 m , mean serum phosphate level was 3.8±0.5 mg/dl, and median (interquartile range) serum C-terminal fibroblast growth factor 23 level was 157 (120-241) relative units/ml. After 12 weeks of treatment, urinary phosphate-to-creatinine ratio fell significantly in the sevelamer group. The sevelamer and placebo groups did not differ significantly in terms of median change in serum C-terminal fibroblast growth factor 23 levels: the median (interquartile range) change was 38 (-13-114) relative units/ml in the placebo group and 37 (-1-101) relative units/ml in the sevelamer group ( =0.77). There was no significant difference in serum intact fibroblast growth factor 23, -klotho, or phosphate levels changes between the two groups. Serum total and LDL cholesterol levels fell significantly in the sevelamer group. In our double-blind, placebo-controlled, randomized study performed in normophosphatemic patients with CKD, a 12-week course of sevelamer carbonate significantly reduced phosphaturia without changing serum phosphorus but did not significantly modify serum C-terminal fibroblast growth factor 23 and intact fibroblast growth factor 23 or -klotho levels.