Faecal pigment derived from chlorophyll has been advocated as an indigestible marker for determining feed digestibility in the grazing animal but has never come into general use. This study now reports that faecal pigment, used in a different way, may be of value in tropical pasture research. In dry-season grasses in the seasonal tropics there appeared to be virtually a complete loss of porphyrins, and animals on such a diet had extremely low faecal pigment levels. However, tropical legumes in current or potential use for improving pastures, even in the dry season, gave rise to high levels of pigment. The difference was so pronounced that faecal pigment may be a sensitive indicator of the amount of legume or other high-quality feed being obtained by the grazing animal on dry-season pasture.