AbstractDifferences among the useful lifetimes of stains are well known to histotechnologists. Though problems of fading have been studied extensively by chemists, these data received little attention in histotechnology. Yet, such information is invaluable for the development of new reactions and modifications of existing technics to improve fastness properties. The history of light fastness determinations, current fastness ratings, light absorption by dyes, and fluorochromes were reviewed in part I of this report. This discussion will deal with relations between structure and fastness properties of dyes, the importance of molecular orbital systems, effects of metals, substrates, moisture, and of various reagents on the fastness, i.e. permanence of stains. (The J Histotechnol12:129, 1989.)