Ultrasound-assisted particle agglutination assay methods and apparatuses are described based on first providing a standing wave ultrasound field at a resonance frequency of a test liquid in a resonator cell containing microparticles covered with a binding agent with high affinity to an analyte sought to be detected by the assay test. Formation of the specifically-bound and nonspecifically-bound aggregates of these microparticles is then followed by effective stirring of the liquid with swept-frequency sonication causing disintegration of nonspecifically-bound aggregates and leaving specifically-bound aggregates in place for further detection and measurement. The methods and devices of the invention allow significant improvement in the sensitivity and specificity of agglutination tests and are advantageously applicable to detecting various proteins, DNA, RNA and other biologically active substances. Specific examples are provided.