An objective, solid-phase fluoroimmunoassay for treponemal antibody was developed with a lysate of virulent Treponema pallidum (Nichols strain) adsorbed on cellulose acetate disks. A probe containing both the antigen and control disks is inserted successively into a serum specimen dilution, a buffer rinse, fluoroscein isothiocyanate-conjugated goat anti-human immunoglobulin G, and a second buffer rinse. Fluorescence signal units are measured with a fluorometer. To establish test calibration

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... es, the corrected fluorescence values (antigen disk minus control) of reference sera are plotted against indirect fluorescent treponemal antibody test titers. The corrected fluorescence values obtained for 62 sera reactive in the fluorescent treponemal antibody absorption test ranged from 64 to 178; values for 66 nonreactive sera ranged from 20 to 46. Thus, the solid-phase fluoroimmunoassay for treponemal antibody clearly separated specimens from patients with documented primary, secondary, or latent disease from fluorescent treponemal antibody absorption-nonreactive sera. The test is technically simple and produces an objective quantitative result.