Thromboembolic occlusions of the cerebral arteries often recanalize spontaneously, and patients with early recanalization have a better outcome than patients who do not recanalize. Clinical as well as experimental data support the concept of a time window within which brain tissue will profit from restoration of blood flow. In occlusion of middle cerebral artery, internal carotid artery, as well as vertebrobasilar arteries, open studies of intra-arterial administration of thrombolytic agents have demonstrated recanalization within hours in 40-100% of patients in small series. In intravenous drug administration, recanalization rate was obtained in 34-59% of patients. Favourable outcome was associated with recanalization. Intracerebral bleeding complications with clinical deterioration occurred in about 10% of patients. Three randomized controlled trials comprising 156 patients with acute ischaemic stroke have reported favourable outcome in treated patients, with no difference of intracerebral haemorrhagic complications between treated and controls. Results of ongoing randomized placebo controlled trials are expected in 1995 to disclose whether a clinical breakthrough is achieved or whether haemorrhagic complications will outweigh a beneficial effect of thrombolytic therapy in acute cerebral ischaemia.