The distal convoluted tubule (DCT) plays key roles in blood pressure (BP) homeostasis. It reabsorbs up to 7% of the filtered sodium load, and its length changes with demand optimizing sodium delivery to the collecting duct. The Na-Cl co-transporter (NCC) is the predominant route for apical entry of sodium into DCT cells and its inhibitors, thiazide diuretics, are mainstay treatments for hypertension. Predictive adaptions of sodium excretory rhythms are supported by an intrinsic renal clock, which may regulate the renal transporters according to physiological need (1). Furthermore, the anti-natriuretic hormones, aldosterone and glucocorticoids have a circadian rhythm which may influence NCC activity (2). Understanding the circadian rhythm of sodium transporters is important for antihypertensive dosing regimens particularly in patients lacking a nocturnal drop in BP (“dip”). C57BL6 mice, implanted with radiotelemetry devices for conscious, unrestrained BP, heart rate (HR) and activity monitoring, were housed in an isolated room with a 12 hour light dark cycle and ad lib access to food and water. Separate cohorts of mice, housed similarly, were rapidly culled by cervical dislocation at 1am or 1pm and kidneys were harvested for Western analysis and qPCR. C57BL6 mice exhibit a circadian rhythm of BP, HR and activity, with significant dipping of these parameters during the day (inactive phase) compared to the night (active phase) (p<0.0001 for mean BP, HR and activity, n=6, paired Student’s t-test). Levels of both Slc12a3 (NCC encoding gene) mRNA and NCC protein in the kidney were similar between night and day (p= 0.31, p=0.52 respectively, n=6, Student’s t-test). However, NCC activity is determined by its phosphorylation (particularly at residues: threonine 53, threonine 58 and serine 71). NCC phosphorylation (at threonine 53) was significantly increased in the active phase (1.01±0.035 AU, mean±SEM) compared to the inactive phase (0.52±0.066 AU, mean±SEM, p<0.0001, n=6, Student’s t-test). This was strongly correlated with the expression of the clock genes: per2 and clock1 (r=0.67, p=017 and r=0.60, p=0.04 respectively, n=6, Pearson’s Correlation (PC)) and glucocorticoid-induced genes: GILZ and SGK1 (r=0.62, p=0.03 and r=0.64, p=0.02 respectively, n=6, PC). There were no correlations between aldosterone-regulated genes (mineralocorticoid receptor and renin) and NCC phosphorylation at threonine 53 (r=-0.11, p=0.72 and r=-0.08, p=0.81, respectively, n=6, PC). NCC phosphorylation has a strong diurnal rhythm, being greater in the active compared to resting phase. The associations with glucocorticoid-regulated genes suggest a role for this hormonal system in the diurnal regulation of NCC.