Technical Abstract: Many plants of the Panicum genus have been reported to cause hepatogenous photosensitization in animals throughout the world (Flaoyen, 2000). Glycosidic steroidal saponins have been found in some species of the Panicum genus and these compounds have been suggested as one of the primary agents causing hepatogenous photosensitization in animals grazing these grasses (Patamalai et al., 1990; Holland et al., 1991; Miles et al., 1992). The hydrolysis of the saponins isolated from plant material yields sapogenins. The sapogenin diosgenin (1) has been identified in P. dichotomiflorum and in P. schinzii (Holland et al., 1991; Miles et al., 1992), while diosgenin (1) and an isomer, yamogenin (2), have been isolated from P. coloratum (Patamalai et al., 1990). In 1992, Puoli et al. (1992) reported hepatogenous photosensitization in lambs grazing switchgrass (Panicum virgatum L. cv. Cave-in-Rock). In the summer of 2000, poisoning of horses grazing a pasture of switchgrass (Panicum virgatum L.) in eastern Nebraska was reported to our laboratory. The purpose of this study was to determine if saponins and their hydrolysis products, sapogenins, were present in the Cave-in-Rock cultivar switchgrass that was reported to cause photosensitization in lambs and in the switchgrass from the pasture where the horses were poisoned. We also analyzed a sample of Kleingrass 75 (Panicum coloratum L.), previously implicated in a photosensitization case.