Two unusual complications, encountered during pulmonary artery catheterization, are described. In both cases the catheter had been introduced percuta-neously with the Seldinger technique. Inadvertent entry of the right pleural space occurred in one case in which the catheter had been inserted into the internal jugular vein through a low cervical approach. The second complication was separation of the shaft of the introducer from the hub, with consequent risk of embolization. Possible means of preventing and treating these complications are discussed.