Abstract: An immunoassay device including one or more reaction chambers, each adapted to receive and retain a volume of test fluid in fluid communication with nonoverlapping first, second, and third reagent-bearing surfaces. To the first surface is reversibly bound an analyte conjugate: analyte component conjugated to one or more components, termed ligand/marker, that serve ligand and marker functions as described herein. Analyte binding partner is immobilized on the second surface, and ligand/marker binding partner is immobilized on the third surface. The reaction chamber is preferably configured to receive and direct the test fluid sequentially past the first second, and third reagent surfaces. In use, analyte conjugate solubilized from the first surface completes with any analyte in the test fluid for analyte binding partner sites on the second surface.