Summary Background LCZ696 is a first-in-class inhibitor of the angiotensin II receptor and neprilysin. We aimed to establish whether the dual actions of LCZ696 lead to further lowering of blood pressure, compared with the angiotensin-receptor blocker valsartan. Methods 1328 patients aged 18–75 years with mild-to-moderate hypertension were randomly assigned (double-blind) to 8 weeks' treatment in one of eight groups: 100 mg (n=156 patients), 200 mg (n=169), or 400 mg (n=172) LCZ696; 80 mg (n=163), 160 mg (n=166), or 320 mg (n=164) valsartan; 200 mg AHU377 (n=165); or placebo (n=173). The primary endpoint was the mean difference across the three single-dose pairwise comparisons of LCZ696 versus valsartan (100 mg vs 80 mg, 200 mg vs 160 mg, and 400 mg vs 320 mg) in mean sitting diastolic blood pressure during the 8-week treatment period. Analysis was by intention to treat. This trial is registered with ClinicalTrials.gov , number NCT00549770. Findings 1215 patients completed the 8-week treatment period. The average reduction in mean sitting diastolic blood pressure across the doses of LCZ696 versus the appropriate comparator dose of valsartan showed significantly greater reductions with LCZ696 (mean reduction: −2·17 mm Hg, 95% CI −3·28 to −1·06; p<0·0001). The reduction in mean sitting diastolic blood pressure was significantly different for 200 mg LCZ696 versus 160 mg valsartan (−2·97 mm Hg, 95% CI −4·88 to −1·07, p=0·0023) and for 400 mg LCZ696 versus 320 mg valsartan (−2·70 mm Hg, −4·61 to −0·80, p=0·0055). LCZ696 was well tolerated and no cases of angio-oedema were reported; only three serious adverse events occurred during the 8-week treatment period, of which none was judged to be related to the study drug, and no patients died. Interpretation Compared with valsartan, dual-acting LCZ696 provides complementary and fully additive reduction of blood pressure, which suggests that the drug holds promise for treatment of hypertension and cardiovascular disease. Funding Novartis.