<p>The present invention relates to a method for performing an immunodiffusion assay comprising at least the following steps of (a) preparing one or more test samples comprising an influenza virus antigen, (b) treating the test samples with at least 5% (w/v) of detergent, (c) applying the treated test samples to a gel comprising an antibody specific to the influenza virus antigen, and (d) allowing the samples to diffuse into the gel.</p>
