Chlorophylls, the green pigments responsible for photosynthesis in plants, algae and bacteria, are also part of the daily diet of herbivorous feeders. Numerous metabolic derivatives of the major green pigment, chlorophyll-a, have been found in a wide variety of organisms during the last decade. Studies of these metabolites show that some are antioxidants or cellular signaling mediators in vivo. The metabolites of bacteriochlorophylls-c and d, recently found in the deep-sea dragon fish, Malacosteus niger, function as a visual photosensitizer, enabling the fish to seek their prey in 'the dark'. Discovery of these metabolites as well as their interesting biological functions raises questions as to the roles of chlorophyll derivatives in the chemical ecology of herbivorous life forms. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.