Only a few investigators have evaluated labeling of the esophageal wall with metallic markers in experimental animals (3, 4, 6) or in the human (1, 2, 7). Usually, implantation of a marker has necessitated thoracotomy or laparotomy. A transesophageal approach, however, avoids possible undesirable, physiologic alterations caused by surgery. The present report describes a transesophageal technic for marking the esophageal wall of cats with small tantalum wires. Such markers permit evaluation of esophageal motility. Materials and Method Marking procedures were performed on 9 cats. The animals were anesthetized with sodium pento–barbital (30 mg'kg intraperitoneally) and secured supine on a board. To permit visualization, the esophageal mucosa was outlined by powdered tantalum, insufflated into the esophagus through a NO.7 French polyethylene catheter (5). The apparatus for implantation of the tantalum wire consisted of a No. 18 needle, 24 cm long, fitted with a steel wire plunger. A single, tantalum wire sliver (diameter 0.4 mm, length 3 mm) was inserted into the end of the needle. The flexible needle was controlled by passing it through a No. 7 French Teflon sleeve attached to a supporting metal rod of 5 mm diameter. Under fluoroscopic control, the apparatus was positioned in the distal esophagus. Lateral displace–ment of the apparatus stretched the mucosa across the mouth of the Teflon sleeve, insuring mucosal engagementas the needle was advanced. The tip of the needle was passed about 1 mm beyond the sleeve until it could be felt to catch in the mucosa. The esophagus was returned to the midline by repositioning the apparatus. Prolapse of the mucosa was prevented by applying countertraction to an inflated Foley balloon in the proximal esophagus. The mucosa was completely penetrated by advancing the needle 3 to 5 mm and, by pushing the plunger, the sliver was expressed into the esophageal wall. Powdered tantalum coating of the mucosa permitted accurate placement of the needle tip and of the tantalum slivers under fluoroscopic control. With this method,8 to 12 slivers were implanted into each esophagus studied (Fig. 1). Three cats were killed immediately after the procedure. The other 6 animals received penicillin 400,000 units and strep tomycin 0.5 gm intra–muscularly daily for live days. Of these 6 cats, 1 was killed at one week, another at two weeks, and a third at four weeks. Three animals prepared early in the study died from mediastinal hematoma or aspiration pneumonitis one to six days after marking. On cine–esophagography of 3 cats one to four weeks after implantation of tantalum sliver, no alterations were observed in the esophageal motility. Examination of the resected esophagi showed most of the tantalum wires to be located in the esophageal adventitia. A few slivers were seen to be in the mediastinum.