A technique used to identify specific proteins in tissue samples by applying antibodies that have been labelled with a fluorescent compound (e.g. fluorescein). The labelled antibody combines with the protein under investigation and the resulting complex can be identified under a microscope by its fluorescence (i.e. immunofluorescence microscopy). Proteins and enzymes in tissue samples can be identified and located in this way. In indirect immunofluorescence the bound antibody is detected by an ‘anti-antibody’ fluorescent immunoglobulin. See also confocal fluorescence microscopy.