Fluorescence has been detected in some white standard tiles intended for the calibration of spectrophotometers for colour measurements. The problem is that usually no warning is given to the user about it, giving raise to errors if they are calibrated using conventional spectrophotometric techniques. This work analyzes the differences on the colour coordinates of one of these standards measured with a polychromatic illumination spectrophotometer and with a monochromatic illumination one. This work also analyzes the colour coordinates error obtained when other coloured standards are calibrated against one of these white fluorescent standards, when reflectance measurement is done with a polychromatic illumination spectrophotometer as well as with a monochromatic illumination instrument. These are the two most typical situations found in practice where the use of fluorescent standards may produce errors. (C) 2004 Wiley Periodicals, Inc.