Can intracoronary thrombolytic therapy (ITT) reduce the infarct size and improve regional and global left ventricular function and if so how long after recanalization does this improvement develop? 42 patients were treated with ITT, of whom 25 showed successful recanalization (group A) and 17 had persistent occlusion or reocclusion (group B). Both groups were examined five times during the first month after infarction with two-dimensional echocardiography. The 'asynergy index' improved in group A by 45% of initial pretreatment values, compared with no significant change in group B (P less than 0.005). The 'asynergy extent' improved in group A by 35%, while in group B again no change was observed (P less than 0.01). This improvement occurred slowly, significant differences being achieved by the 10th day. Entire normalization of left ventricular wall motion was observed in 5 patients (20%) from group A and in no patient from group B. We conclude that successful recanalization of the occluded coronary artery by ITT improves left ventricular wall motion in 80% of patients, with entire normalization of local function in 20% of cases. The improvement occurs slowly during the first 10 days.