Method for the demonstration of a specific complex formed by reacting an antibody present in a solution and an antigen bound to a magnetic particle, the reaction taking place in a reactor with an open top and sealed base whose diameter decreases at least in the area close to the base in such a way that it forms an inclined wall extending down to the base, said inclined wall being at least partially coated with an anti-immunoglobulin or any other compound capable of binding to the antibody of said formed complex, characterised in that it comprises the following steps: a) Prior to the reaction, - preliminary filling of the reactor with a viscous substance or homogeneous gel such that at least part of the inclined wall of the reactor is coated, wherein said viscous substance or said homogeneous gel has density such that it prevents the migration of antibodies which do not form complexes with the antigens bound to the magnetic particles towards the wall coated with anti-immunoglobulin or any other compound capable of binding to the antibody during step d), b) contacting the solution containing or likely to contain said antibody with the magnetic particle suspension carrying or likely to carry said antigen at a point above the viscous solution in the reactor, c) incubation of the reactor, preferably for the period of time required for the formation of the complex, d) application of a magnetic field to said reactor and stirring of the reactor such that the magnetic particles are either drawn towards the base and/or inclined wall of the reactor, and e) reading with the naked eye and/or by any other suitable reading system of the image obtained at the base of the reactor and/or inclined wall of the reactor coated with said anti-immunoglobulin or any other compound capable of binding to the antibody, the image obtained making it possible to demonstrate the presence or otherwise of the formation of a specific antibody/antigen complex. a) Prior to the reaction, - preliminary filling of the reactor with a viscous substance or homogeneous gel such that at least part of the inclined wall of the reactor is coated, wherein said viscous substance or said homogeneous gel has density such that it prevents the migration of antibodies which do not form complexes with the antigens bound to the magnetic particles towards the wall coated with anti-immunoglobulin or any other compound capable of binding to the antibody during step d), - preliminary filling of the reactor with a viscous substance or homogeneous gel such that at least part of the inclined wall of the reactor is coated, wherein said viscous substance or said homogeneous gel has density such that it prevents the migration of antibodies which do not form complexes with the antigens bound to the magnetic particles towards the wall coated with anti-immunoglobulin or any other compound capable of binding to the antibody during step d), b) contacting the solution containing or likely to contain said antibody with the magnetic particle suspension carrying or likely to carry said antigen at a point above the viscous solution in the reactor, c) incubation of the reactor, preferably for the period of time required for the formation of the complex, d) application of a magnetic field to said reactor and stirring of the reactor such that the magnetic particles are either drawn towards the base and/or inclined wall of the reactor, and e) reading with the naked eye and/or by any other suitable reading system of the image obtained at the base of the reactor and/or inclined wall of the reactor coated with said anti-immunoglobulin or any other compound capable of binding to the antibody, the image obtained making it possible to demonstrate the presence or otherwise of the formation of a specific antibody/antigen complex.