Biobest Laboratories produces immunofluorescence assay (IFA) test plates and slides by immobilising cells infected with virus or parasitic tachyzoites by chemical fixation. Samples are added to the test plates or slides at several dilutions and incubated at core body temperature; if antibodies to the antigen are present in the sample they will bind to the antigen during this incubation (Figure 1). The tests are washed to remove any antibodies which have not bound then a suitable anti-species antibody conjugated to a fluorescent marker is added. this secondary antibody will bind to any antibodies which were present in the sample and had bound to the antigen. The tests are incubated then washed again before being read by microscopy using ultra violet illumination. The fluorescent marker glows with a bright apple green fluorescence under the UV light indicating the presence of specific antibodies bound to the antigen (figure 2). The pattern of fluorescence observed often confirms the specificity of the reaction. The sample antibody titre is the last dilution of the sample to show this specific fluorescence.