To the Editor: Mansfield et al. (Dec. 29 issue)1 found that ultrasound-guided location of the subclavian vein was not beneficial, as compared with standard insertion procedures for subclavian-vein catheterization. The authors used ultrasound only to mark the site of insertion and did not study real-time ultrasound guidance of catheter placement. We believe that real-time ultrasound guidance might have been beneficial because of the favorable findings of another study2 and the reported success with ultrasound guidance of internal jugular-vein catheterization.3—5 A simple mark on the skin does not indicate the axis that will engage the vessel. The deeper the structure,.