An outbreak of mortality in a flock of mutton merino sheep in which 109 out of 568 sheep died in the south-western Cape Province [Republic of South Africa], is described. It was characterized by hemorrhagic septicemia, anemia, leucocytopenia and hemorrhagic tendencies. Mortalities followed unseasonal and heavy summer rain, extended over a period of 6 mo. and were associated with the uninterrupted consumption of sheep cubes processed on the farm from severely fungus-infested wheat, barley and rye straw for a period of at least one mo. The main clinical signs occurred in 2 phases: an elevated body temperature, listlessness, epistaxis and intermittent hemorrhagic diarrhea during the 1st phase of the outbreak, and a progressively worsening anemia, leukocytopenia and less severe hemorrhagic tendencies and a terminally elevated body temperature during the 2nd phase. The predominant autopsy findings were purpuric hemorrhage on serosal and mucosal surfaces and in most of the organs, enterorrhagia and severe pulmonary congestion and edema during the 1st stage; anemia was the predominant sign during the second state - widespread hemorrhage still occurred but was less extensive. Pasteurella haemolytica was isolated from most of the animals autopsied during the first stage. Histologically, the most salient features were atrophy and necrosis of the lymphoid tissue, aplastic anemia and a markedly impaired inflammatory response. Extensive post-natal lamb mortalities, probably due to an Escherichia coli infection precipitated by the toxicosis, occurred during the outbreak. Toxigenic strains of Stachybotrys chartarum were isolated from the wheat and barley straw. Diethyl ether extracts of the wheat straw, sheep cubes and S. chartarum culture material elicited positive skin tests in rats following intradermal injection and the presence of 12,13-epoxytrichothecenes in these extracts were confirmed by TLC. In feeding trials sheep cubes and wheat straw caused the death of 4/4 1-day-old Pekin ducklings and weanling Wistar rats in 6 and 9 days, respectively.