The visualisation of an antigen in a histological section or on a polyacrylamide slab by allowing it to combine with a fluorophore-tagged antibody. In indirect immunofluorescence the antibody is not itself labelled but is the target of another antibody which is labelled, e.g. detection of an antigen by a specific human antibody that depends upon the subsequent attachment to the antigen-(human antibody) complex of a rabbit antibody directed against a broad range of human immunoglobulins.