Our objective was to assess the effects of supplementation with oral potassium on blood pressure (BP) in humans, using pooled analysis of randomized, controlled trials. Results from 33 randomized, controlled trials (2,609 participants) in which potassium supplementation was the only difference between the intervention and control conditions were used. Information on sample size, duration, study design, potassium dose, participant characteristics, and treatment results was independently obtained by the authors using a standardized protocol. The findings from each trial were pooled after weighting the results for individual studies by the inverse of its variance. Using a random-effects model, potassium supplementation was associated with a significant reduction in mean (95% confidence interval) systolic and diastolic BP of -4.44 (range, -2.53 to -6.36) and -2.45 (range, -0.74 to -4.16) mm Hg, respectively. After exclusion of a trial with extreme results, potassium supplementation was still associated with a significant reduction in mean (95% confidence interval) systolic and diastolic BP of -3.11 (range, -1.91 to -4.31) and -1.97 (range, -0.52 to -3.42) mm Hg, respectively. The BP effects of potassium administration appeared to be enhanced in studies where participants were concurrently exposed to a high intake of sodium. Increased potassium intake should be included as a recommendation for prevention and treatment of hypertension, especially in those who are unable to reduce their intake of sodium.