Animal evidence shows that aldosterone is pro-inflammatory and that aldosterone blockade is anti-inflammatory. Therefore part of the beneficial effect of aldosterone blockade that might contribute to it reducing mortality could be an anti-inflammatory effect. However, there are no previous data on whether aldosterone blockade is anti-inflammatory in man. We performed 4 separate studies to investigate whether spironolactone treatment would reduce levels of C-reactive protein (CRP), a marker of inflammation, in serum samples taken from patients suffering from different degrees of heart failure. We found in all 4 studies that spironolactone had no significant effect compared with placebo, on CRP levels in these patients. These studies provide evidence against the hypothesis that the clinical benefits produced by aldosterone blockade are due to it having anti-inflammatory effects.