Abstract: An immunoassay method for the detection of an antibody (Ab.sub.1) to a viral antigen (Ag) wherein a whole human blood sample diluted with an isotonic aqueous solution is incubated with a solid-phase form of Ag whereby any Ab.sub.1 present in the sample becomes bound to solid-phase Ag, the resulting solid-phase Ag-Ab.sub.1 complexes are separated from the sample, a label-incorporated form of an antibody to Ab.sub.1 (Ab.sub.2 *) is contacted with the separated, solid-phase Ag-Ab.sub.1 complexes, the resulting solid-phase Ag-Ab.sub.1 -Ab.sub.2 * complexes are separated from excess Ab.sub.2 *, and the amount of the label in the separated, solid-phase Ag-Ab.sub.1 Ab.sub.2 * complexes is measured as a function of the presence of Ab.sub.1 in the sample. Preferably the whole blood sample is diluted 1:20 by volume with an isotonic aqueous buffer solution. The method is particularly useful for the detection of cytomegalovirus antibody or Rubella antibody.