In the European Cooperative Acute Stroke Study 3 (ECASS3), the efficacy of intravenous thrombolysis between 3 and 4.5 hours following onset of ischaemic stroke was investigated. Compared to the placebo group, patients treated with intravenous alteplase had a better functional outcome after 3 months (odds ratio 1.34, 95% confidence interval 1.02-1.76). The risk of symptomatic intracerebral haemorrhage was higher in the alteplase group (2.4% versus 0.3%). The time window for intravenous alteplase can be safely extended to 4.5 hours, but efforts should be made to start treatment as soon as possible, since the effectiveness ofalteplase decreases over time.