Nitric oxide is a multimodal candidate treatment for acute stroke having a number of properties which may be beneficial in acute stroke, including lowering blood pressure, causing cerebral vasodilation, and improving central and systemic haemodynamics. Nitric oxide donors are effective in experimental stroke and pilot studies in patients suggest that one, glyceryl trinitrate, can be delivered easily in a transdermal preparation. Around half of all patients admitted with acute stroke are taking antihypertensive therapy immediately prior to their stroke. No data exist as to whether it is beneficial or safe to stop or continue this treatment during the acute phase. ENOS is a prospective, international, multicentre, randomised, parallel-group, blinded, controlled, collaborative, factorial trial designed to test two questions related to the management of blood pressure immediately post-stroke: