One in five strokes occur during sleep, but patients with "wake-up" stroke are not given thrombolytic therapy because time of stroke onset is unknown. On-going trials are testing alteplase, and use MRI techniques for selection of patients. Tenecteplase has many pharmacological advantages over alteplase: greater fibrin specificity, very rapid action, longer half-life, and single bolus administration. In addition, patient selection based on MRI findings risks excluding many patients that might otherwise benefit. TWIST will test tenecteplase and will not use MRI techniques for selection of patients. Plain CT and CT angiography (if possible) will be performed before randomisation, and CT perfusion will be performed at selected centres, as part of a sub-study.