The ultrasonographic appearance of different plastic catheters, tubes, and prostheses used in medical practice were tested in vivo and in vitro. According to the direction of the sound beam, the different plastic catheters and tubes appeared as parallel echogenic lines if scanned longitudinally, or as echogenic dots if scanned transversely. The exact position of the tip of the catheter and its relationship to neighboring organs can be established by ultrasonography. Repositioning of tubes, if necessary, can be done under ultrasonographic guidance. The flexibility and mobility of modern ultrasound scanners allows one to examine the sick patient with minimal disturbance, and to evaluate the location and effect of the various plastic catheters and tubes inserted into the body for medical reasons.