During February 1975, a tremorgenic neurotoxicosis decimated a herd of cattle in the northern Transvaal. This hitherto unidentified disease was characterized by hypersensitivity, incoordination, a peculiar stiff-legged gait of the hind legs, severe generalized tumors of the sketetal muscles, progressive paresis, paralysis and constipation. The most notable gross pathological lesions were degenerative and necrotic changes in certain skeletal muscles, haemorrhages on the serosal surfaces, especially on the dorsal aspect of the rumen, and gastro-intestinal stasis. Microscopical examination of the central nervous system revealed cytopathological changes consisting of degeneration and necrosis of the large motor cells in the ventral horns of the spinal cord and bigger neurones in numerous nuclei of the medulla oblongata, midbrain and thalamus. By feeding the suspect ration and its component parts to cattle and sheep, it was possible to identify mouldy sorghum beer residue as the toxic component in the ration. A. clavatus, the dominant fungus on the toxic residue, was readily isolated in pure culture. The entire syndrome was then reproduced in a yearling Friesland steer dosed with pure cultures of the A. clavatus isolate grown on autoclaved non-toxic sorghum beer residue. The toxic principle is not known, but it does not appear to be patulin, tryptoquivalone, tryptoquivaline, or any other known tremorgen.