The question whether the silver copper wire of Nova-T (0.1 mm silver core and 0.1 mm copper medication) or the pure copper wire of ML Cu 250 short with 0.4 mm copper present a long-term improvement of intrauterine devices (IUDs) was investigated. Previous IUDs showed copper fragmentation since the diameter of their copper wires were only 0.2 mm to 0.3 mm. 350 copper IUDs were studied for corrosion by electron- microscopy and by gravimetric measurement of loss of mass. Average values at start were: 120 mg copper mass 20 mg silver mass 211 sq mm copper surface for the Nova-T and 230.5 mg copper mass and 276 sq mm copper surface for the ML Cu 250 short. The amount of variation of surface and crack corrosion was great depending on the duration of use. In the 5th year of use in a large number of silver-core copper wires the copper corrosion process reached the silver core and silver core was fully laid bare. Wire fragmentation was not observed until the 6th year of use neither in Nova-T nor in ML Cu 250 short. The median copper corrosion rate vs 21.3 +or- 11 mg for Nova-T and 47.5 +or- 23 mg for ML Cu 250 short. The ML Cu 250 short devices had higher corrosion rates for 100 sq mm copper wire surfaces. A linear process of mass loss could be demonstrated by regression analysis for both IUDs. On the whole both the Nova-T and ML Cu 250 short devices are suitable for a 5 year lifetime use nonetheless the ML Cu 250 short device had advantages for contraception both for short-term and long-term use because of its larger amount of copper medication.