Aim: Is once daily low dose extended release niacin effective at lowering phosphate? Background: Serum phosphate levels correlate with mortality in dialysis patients. Current phosphate binders often cause side-effects leading to poor compliance. Niacin has previously been shown to lower serum phosphate in patients with kidney disease. However, at doses previously used (≥ 1 g daily), it is poorly tolerated. Slo-niacin® is a extended release formulation taken once daily. Methods: The study was a single-centre double-blind placebo-controlled randomised cross-over trial in haemodialysis patients. All patients received both active treatment (500 mg Slo-niacin® daily) and matching placebo for 8 weeks each with intervening 2 week washout phase. All patients continued usual phosphate binders and Cinacalcet/vitamin D analogues, although no dose adjustments were permitted. Patients were recruited if they were >18yo, not pregnant and serum phosphate 4 weeks prior to commencement was ≥ 1.8 mmol/L. All gave informed consent. Results: 33 patients were recruited. 1 patient died following emergency cardiac surgery during placebo phase & 3 patients withdrew (2 niacin, 1 placebo, p=NS) leaving 29 for analysis. Extended release niacin significantly reduced serum phosphate compared to placebo (p<0.0014, t-test and ANOVA). Mean absolute difference between groups was -0.35 mmol/L (95% CI -0.62 mmol/L to -0.08 mmol/L) in favour of niacin (p ~ 0.01, t-test). Neither treatment altered calcium levels. Extended release niacin was well tolerated apart from early mild flushing which improved with time. Conclusion: Once daily low dose extended-release niacin is effective at lowering serum phosphate.