The development of the fluorescent treponemal antibody-absorption (FTA-ABS) test1 has been the result of continued attempts to improve the original FTA procedures,2,3 in terms of sensitivity and specificity. Test improvement was made possible by the discovery that nonpathogenic treponemes such as Treponema microdentium and the Reiter treponeme share antigens in common with T pallidum, and the corresponding common antibodies are of frequent occurrence in serums from normal individuals. It was found, however, that such antibodies could be removed from test serums by intact Reiter treponeme absorption and that in serums so treated and subsequently examined there was an increased specificity and sensitivity of test results.4 Later, the use of sonic-disrupted Reiter treponemes in place of intact organisms for absorption was described, the resulting procedure being identified as the FTA-ABS test.1 At present, a stable water-soluble extract from Reiter treponemes is employed instead of sonicate. This change