The effect of mineral deposits on the copper dissolution rate of the Copper T Model TCu22OC was examined. 118 Copper T22OC devices removed from subjects for various medical and personal reasons after 12 to 72 months in utero were examined and graded based on the proportion of the total copper area covered with mineral deposits. The deposits increased in average size during the first three years of IUD use and then remained relatively constant. Seventeen percent of the devices were in situ for four or more years. Copper analysis was performed on 30 Copper T 22OC devices from selected periods of use : 12-14, 22-26, 36-39 and 48-72 months of use. The mean daily copper loss was 29.4 micrograms and the range, 7.3 to 62.1 micrograms. An inverse correlation between the amount of mineral deposit on the copper surface and the rate of copper loss was observed.