Using transoesophageal echocardiography, large aortic masses were found to be rigidly attached to the aortic wall in two patients—in one patient the masses extended from the aortic arch to the descending aorta, while in the other patient the masses extended from the descending thoracic to the abdominal aorta. Intraluminal two dimensional ultrasound was then used to guide percutaneous biopsies of these aortic masses. First, a long 11 French access sheath was conventionally introduced into the left femoral artery and advanced to the descending aorta. A phased array transducer tipped AcuNav-Catheter (Siemens-Acuson Inc) was then inserted through the access sheath so that only the tip of the catheter with the transducer was allowed to leave the sheath. Next, the access sheath with the AcuNav-Catheter inside was slightly withdrawn and the transducer adjusted to the distal end of the mass by observing the ultrasonographic images (left panel). Under continuous ultrasonographic viewing, each three targeted biopsies were taken from the depth of the masses (right upper panel) using a radial-jaw-biopsy-forceps (Boston Scientific Inc), previously inserted via an 8 French multi-purpose guiding catheter which was introduced through a second access sheath from the right femoral artery. Opening, pushing, and closure of the biopsy forceps were precisely guided and documented (right lower panel). No complications were observed. In addition to fresh fibrin and erythrocytes, histological analyses revealed connective tissue with fibroblasts and macrophages in all six specimens.