The authors report their experience with cine-MRI in evaluating the infiltration of the main cardiovascular structures by expansive mediastinal masses. Twenty-four patients with proven lung (12 cases) and mediastinal (12 cases) cancers, previously selected with CT, underwent MRI examination of the chest. A superconductive 1.0 T unit was employed. Cytohistologic confirmation was obtained in all cases (6 thymomas, 6 lymphomas, 12 lung cancers). Ten normal subjects were also studied as a control group. Axial, coronal, and sagittal SE T1 images were obtained as the basis for MRI investigation of the chest. Subsequently, gradient-echo pulse-sequences images were obtained during the whole cardiac cycle, and later displayed on cine-Mode, on the section plane where vessel wall was closest to the tumor. The results prove cine-MRI to allow a correct diagnosis to be made in all cases, especially in those patients where CT and conventional SE MRI yielded questionable results. This preliminary experience suggests that cine-MRI could be used as a complementary method to CT and conventional SE MRI in evaluating mediastinal vessel involvement.