Both epidemiologic and clinical studies have suggested that an increase in potassium intake may lower blood pressure. However, the results of prospective clinical trials looking at the effect of oral potassium supplements on blood pressure have yielded conflicting results. For this reason, we reviewed 19 clinical trials examining the same end-point and involving a total of 586 participants (412 of whom had essential hypertension). Overall, the results of the trials indicate that oral potassium supplements significantly lower systolic blood pressure [-5.9 mmHg, -6.6 to -5.2 mmHg (mean, 95% confidence interval)] and diastolic blood pressure (-3.4 mmHg, -4.0 to 2.8 mmHg). The magnitude of the blood pressure lowering effect is greater in patients with high blood pressure (-8.2 mmHg, -9.1 to -7.3 mmHg for systolic and -4.5 mmHg, -5.2 to -3.8 mmHg for diastolic blood pressure) and appears to be more pronounced the longer the duration of the supplementation (P less than 0.05 and P less than 0.01 for systolic and diastolic, respectively). Based on this analysis, an increase in potassium intake should be included in the recommendations for a non-pharmacological approach to the control of blood pressure in uncomplicated essential hypertension.