Besides bio-compatibility, mechanical properties are most important requirements of elastomeric polymers used for central vein catheters. We have examined central venous catheters before and after insertion, with the function of insertion time (0-326 days) regarding mechanical changes of properties and surface. The catheters made of thermoplastic polyether-urethane, Pellethane 2363 shore A 90 with the admixture of 10 % barium sulphate for radiopacity. ID/OD, 1.10/1.65 mm. Property changes were determined by Mechanical Testing Apparatus and SEM (Scanning Electron Microscopy). The tensile strength at break diminished to 54 % after 326 days compared to that of the non-implanted. Its elongation increased gradually up to 41 days when it was 188 % higher. 326 days after insertion the elongation at break was 72 % lower compared to unused catheters. In SEM, fissures with a depth of maximum 26 µm were detected in the surfaces of the indwelling catheters. The stiffness decreased slightly. After 326 days it became 67.48 % of the stiffness of the unused catheter. The surface of the catheters showed surface interactions, penetration, absorption, swelling, wrinkles and crazes.