The abdominal portion of the aorta was catheterized in 27 cows. Local analgesia was achieved by infiltration of anesthetic agents. A 10-cm skin incision was made caudal and parallel to the 13th rib at the lateral border of the epaxial muscles. The dorsal costoabdominal artery was exposed at its first lateral cutaneous branch by careful dissection through fascial layers. A sterile polyvinyl catheter (1.52 mm OD) was inserted into the artery and was advanced 35 to 40 cm to the abdominal portion of the aorta. Catheter patency was maintained for up to 5 weeks. Concentrations of plasma progesterone and estradiol-17 beta in samples obtained from the abdominal portion of the aorta were similar to simultaneously obtained concentrations in samples from the jugular vein before and after parturition.