Abstract: The invention is a method for grading a polyclonal antibody response with respect to a desired 5 binding specificity. The response is provoked by an antigenic agent in a host, preferably a vertebrate host. The characteristic feature of the method comprises the steps of: (i) providing a reaction microcavity having an inlet end and an outlet end and containing a solid phase that exposes an immobilized binding structure (BS) that are capable of affinity binding antibodies (Ab) of the response, (ii) flowing a liquid sample containing antibodies of the response in the direction from the inlet end to the outlet end through the solid phase, (iii) determining the distribution of antibodies, which are captured during step (ii), along the flow direction of the solid phase, and (iv) grading the response based on the distribution determined in step (iii).