Aallegations of livestock illness following consumption of such moldy are associated toxin may be responsible. This study was instigated by field observations of epatogenous photosensitization in cattle fed alfalfa-grass forage. To document the toxic nature of the hay, large beles of hay (450 kg) were fed.ad libitum,to 3 groups of 2 calves each.Elevated serum liver enzymes provided evidence of hepatobiliary disease. Gamma glutamyl transfease activities in serums of the calves sustained at least. Histologic examination of live biopsies and postmortem sections revealed mild periportal fibrosis and biliary hyperplasia.Culture material from 12 fungal isolates from the hay failed to induce liver disease in calves.