Double immunoenzymatic labelling of routinely processed human tissues has been used in many histopathology laboratories to compare the expression patterns of pairs of antigenic markers. However, these techniques are time-consuming, prone to background staining, and rarely suitable for detecting two antigens present at the same site, since one label tends to obscure the other. This paper reports the use of immmunofluorescence for double labelling of pairs of molecular markers in routinely processed tissue. The primary antibodies are either monoclonal reagents of differing isotype/subclass, or antibodies from different species, and labelling is visualized on a conventional fluorescence microscope equipped with a cooled CCD camera. Images can be captured and adjusted using personal computer hardware and software. This approach could be used for a wide range of tissue markers and only minimal tissue autofluorescence was observed. The procedure is more rapid than enzyme-based techniques and avoids the problems of interpreting two antigens present at the same site. Its establishment involves relatively minor expenditure and it may represent the optimal technical approach to the co-localization of pairs of antigens in routinely processed tissue samples.