Abstract: Diagnosis of Lyme disease by immunoassay for anti-Borrelia burgdorferi antibodies in the serum of a patient includes adsorption of crossreactive antibodies in the serum with antigen of Acinetobacter calcoaceticus or Treponema phagedensis prior to binding of anti-Borrelia antibodies to Borrelia burgdorferi antigen absorbed onto a solid support. The preferred assay is a flow-through assay using a porous membrane as the support and a dye-loaded liposome conjugated to a goat antihuman antibody for detection. The invention includes a kit of materials for performing the assay.