For 13 patients with subacute and 4 patients with chronic occlusion, magnetic resonance imaging (MRI) of occlusive arterial thrombi in the superficial femoral artery were performed in vivo. The patients with subacute occlusion were treated with catheter-directed thrombolysis. The frequency of MR signal intensity and its distribution in thrombi were studied for 11 successfully and 2 unsuccessfully treated patients and patients with chronic occlusion. Intra-arterial thrombi were MRI inhomogenous in all of the patients, but the MR signals from lysable and chronic thrombi were significantly different than those from nonlysable ones. The MRI of occlusive arterial thrombi is probably usable to predict the therapeutic outcome of thrombolytic treatment.