There is growing evidence from epidemiological studies that dietary protein may beneficially influence blood pressure (BP), but findings are inconclusive. We performed a meta-analysis of 29 observational studies and randomized controlled trials (RCTs) of dietary protein and types of protein in relation to BP or incident hypertension, published until January 2012. The analysis included eight cross-sectional studies (n = 48 985), four prospective studies (n = 11 761) and 17 RCTs (n = 1449). A modest inverse association between total protein intake and BP ( 0.20 mm Hg systolic (95% CI: 0.39, 0.01) per 25 g (similar to 1 s.d.)) was found in cross-sectional studies, but not in prospective studies (relative risk of 0.99 (95% CI: 0.96, 1.02)). For RCTs that used carbohydrate as a control treatment, the pooled BP effect was -2.11 mm Hg systolic (95% CI: -2.86, -1.37) for a weighed mean contrast in protein intake of 41 g per day. A non-significant inverse association of -0.52 mm Hg systolic (95% CI: -1.10, +0.05) per 11 g (similar to 1 s.d.) was found for plant protein in cross-sectional studies, whereas animal protein was not associated with BP. In prospective studies and RCTs, however, the associations of plant protein and animal protein with BP were broadly similar. These findings suggest that increasing the intake of protein at the expense of carbohydrates may have a beneficial effect on BP. The BP effect of specific types of protein remains to be established.