BACKGROUND: Angiotensin II type 1 receptor blockers (ARBs) lower blood pressure (BP) and proteinuria and reduce renal disease progression in many-but not all-patients. Reduction of dietary sodium intake improves these effects of ARBs. Dietary potassium intake affects BP and proteinuria. We set out to address the effect of potassium intake on BP and proteinuria response to losartan in non-diabetic proteinuric chronic kidney disease (CKD) patients. METHODS: We performed a analysis of a placebo-controlled interventional cross-over study in 33 non-diabetic proteinuric patients (baseline mean arterial pressure and proteinuria: 105 mmHg and 3.8 g/day, respectively). Patients were treated for 6 weeks with placebo, losartan and losartan/hydrochlorothiazide (HCT), combined with a habitual (∼200 mmol/day) and low-sodium (LS) diet (<100 mmol/day), in randomized order. To analyse the effects of potassium intake, we categorized patients based on median split of 24-h urinary potassium excretion, reflecting potassium intake. RESULTS: Mean potassium intake was stable during all six treatment periods. Losartan and losartan/HCT lowered BP and proteinuria in all treatment groups. Patients with high potassium intake showed no difference in the BP effects compared with patients with low potassium intake. The antiproteinuric response to losartan monotherapy and losartan combined with HCT during the habitual sodium diet was significantly diminished in patients with high potassium intake (20% versus 41%, P=0.011; and 48% versus 64%, P=0.036). These differences in antiproteinuric response abolished when shifting to the LS diet. CONCLUSIONS: In proteinuric CKD patients, the proteinuria, but not BP-lowering response to losartan during a habitual high-sodium diet was hampered during high potassium intake. Differences disappeared after sodium status change by LS diet.