The aim of this non-randomized study was to investigate whether there is any benefit in the extension of antimicrobial treatment in patients with left-sided native valve endocarditis in whom C-reactive protein levels are still elevated after a standard course of therapy. There was no statistically significant difference in outcome between the group of patients in which treatment was extended in comparison to the group in which treatment was ended at the recommended time. It is unlikely that there is much to gain from extending treatment based on elevated C-reactive protein levels alone.