PIP: This study determines whether the effective surface area and surface condition of a copper IUD are influenced by any changes produced by the biological environment. The Copper 7 (Cu 7) device was used in the experiment. Made from a copolymer of polypropylene and polyethylene with barium sulfate to make it radiopaque, Cu-7 is shaped like the numeral 7 and is wrapped around the stem with 89 mg of copper wire. 16 Cu 7 devices, some used for several months and others as received were examined optically and with the scanning electron microscope. STEM was used to examine 1 device which had been in place for 6 months while an energy-dispersive x-ray analysis (XES) was used to search for copper and other suspected elements in 1 specimen that had been in use for 5 months. All optically examined specimens exhibited signs of a surface deposit. A deposit several micrometers thick was spotted on the wire in the used IUD examined; there was no such layer on the as-received device. The layer appeared very tenacious and impervious in nature at higher magnification. The presence of calcium only was detected by the XES spectrum. The fact that the calcium-rich layer maintains its tenacity even after rinsing in water suggests that it is insoluble in water and is probably calcium carbonate. Calcium deposition on the IUD could occur during menstruation with its accompanying flow of blood and cellular debris; calcium itself is necessary for blood coagulation, about 10 mg/dl of calcium ion being found in the plasma. Calcium deposits in the IUD could reduce the rate at which copper ions are introduced into the physiological systems and may account for device failures which occur at the rate of 1.1-1.5/100 users.