['We sought to evaluate the impact of the speed of recanalization on the evolution of diffusion- weighted imaging (DWI) lesions and outcome in stroke patients treated with tissue-type plasminogen activator (tPA).', 'We evaluated 113 consecutive stroke patients with a middle cerebral artery occlusion who were treated with intravenous tPA. All patients underwent multiparametric magnetic resonance imaging studies, including DWI and perfusion-weighted imaging before and 36 to 48 hours after administration of a tPA bolus. Patients were continuously monitored with transcranial Doppler during the first 2 hours after tPA administration. The pattern of recanalization on transcranial Doppler was defined as sudden (<1 minute), stepwise (1 to 29 minutes), or slow (>30 minutes).', 'During transcranial Doppler monitoring, 13 (12.3%) patients recanalized suddenly, 32 (30.2%) recanalized in a stepwise manner, and 18 (17%) recanalized slowly. Baseline clinical and imaging parameters were similar among recanalization subgroups. At 36 to 48 hours, DWI lesion growth was significantly (P=0.001) smaller after sudden (3.23+/-10.5 cm(3)) compared with stepwise (24.9+/-37 cm(3)), slow (46.3+/-38 cm(3)), and no (51.7+/-34 cm(3)) recanalization. The slow pattern was associated with greater DWI growth (P=0.003), lesser degree of clinical improvement (P=0.021), worse 3-month outcome (P=0.032), and higher mortality (P=0.003).'] Does speed of tPA-induced clot lysis predict DWI lesion evolution in acute stroke?