Abstract. Cholangiohepatopathy was induced in 5 lambs by oral administration of extracts from signal grass (Brachiaria decumbens) in Brazil. Grossly there were pale foci multifocally distributed throughout the hepatic parenchyma in 4 lambs. The microscopic changes, which were similar to those produced by other steroidal sapogenins-containing plants such as Tribulus terrestris and Panicum spp., included multifocal cholangitis, bile duct proliferation, and the presence of crystals in the biliary system. Sporadic outbreaks of photosensitization in ruminants grazing on signal grass (Brachiaria decumbens) have been reported. 9,21 Cases of photosensitization occurring on this grass in Brazil had formerly been ascribed to intoxication by sporidesmin from spores of the saprophytic fungus Pithomyces chartarum. 2,7,8 However, the potential importance of steroidal saponins present in B. decumbens has been established, suggesting that photosensitization by this grass belongs to the group of plant-induced hepatogenous photosensitizations, 9,21 which are also induced by Panicum spp., 3,10,19 Tribulus terrestris, 11,16 Agave lecheguilla, 4 and Narthecium ossifragum. 17 All of these plants contain steroidal saponins and have been associated with cholangitis and deposition of crystals in the biliary system, causing photosensitization in sheep. Furthermore, steroidal sapogenins have been isolated from bile and biliary crystals of sheep fed those plants. 4,10,16,17 The plant saponins are converted by ruminal metabolism into -D-glucuronides of sapogenins, which in the presence of calcium may precipitate, forming the characteristic biliary crystals. 14,21 Diosgenin and yamogenin have been detected from B. decumbens samples and from a mixture of metabolites in the rumen of sheep grazed on B. decumbens. 6,12,14,20 The arguments against involvement of P. chartarum in most Brazilian outbreaks include the low density or even absence of spores and the failure of most fungal isolates to produce sporidesmin. 5,6,[13][14][15]21 Typical photosensitivity has been reproduced in sheep grazing pure pastures of B. decumbens with no detected P. chartarum spores. 6 The aim of the present study was to reproduce hepatic lesions and photosensitization in sheep by oral administration of fractionated extracts from B. decumbens, as has been done with T. terrestris, 11,16 A. lecheguilla, 18 and N. ossifragum. 1 Counts of P. chartarum spores 15 were performed on pasture samples of plant material used for extraction. Forty kilograms of air-dried samples of B. decumbens were powdered and extracted by maceration, using 80 liters ethanol for 7 days at room temperature. A second maceration was performed, and the extracts were mixed. The solvent was evaporated, and the residual alcoholic phase was suspended in water and partitioned with dichloromethane, yielding the dichloromethane and aqueous fractions. After concentration in vacuum and at low temperature (Ͻ55 C), those fractions resulted in 500 g and 1.6 kg of syrupy residues, respectively, which corresponde...