There is an increasing interest in the effect of dietary lipids on the fatty-acid composition of animal tissue lipids, and long-chain fatty acids may make a substantial contribution to the nutritive value of the diet. A cow at pasture may ingest as much as 450 g of lipid in a day (Garton, 1960a) and a recent study reported the influence of pasturefeeding on the body-fat composition of horses (Bowland & Newell, 1974). Most of the data on the fatty-acid composition of pasture lipids are for clover-rich pastures and mixed pasture grasses grown in temperate climates (e.g. Garton, 1960b). By contrast, the lipid composition of tropical pastures has been neglected. This paper reports the seasonal changes in the lipid content and fatty-acid composition of eight species of tropical pasture plants.