This in vitro study investigated the retention of the four differenct color-coded ERA attachments prior to and after various levels of fatigue loading (at baseline, at 500 cycles, and after every 500 cycles up to 5,500 cycles). Samples were placed in the Instron testing machine for determination of initial retentive values and then cycled in a specailly designed fatigue machine and retested. The results of this study demonstrated that although there are fuor different retentive elements supplied by the manufacturer of the ERA system, there were only two significantly different groups: (1) the white attachments and (2) the orange, blue, and gray attachments (P .05). After 500 cycles, there was a loss in retention of 60% for the white, 60% for the orange, 56% for the blue, and 54% for the gray. After 1,500 cycles there was no difference in retentive values for any of the four colored attachments (P .05). Microscopic examination of worn spcimens supported the findings of the fatigue testing.