The clinical responses of sheep dosed orally over seven to 14 weeks with the dried mycelium of a soil-borne mould containing the tremorgenic mycotoxin penitrem A are described. An initial tremoring response was gradually overshadowed by an incoordination syndrome similar to that seen in ryegrass staggers. In spite of protracted staggers symptomatology, correlated with in vitro changes in the release of neurotransmitter amino acids from corpus striatum nerve ending preparations, no histopathology was evident in the wide range of neural and other tissue studied. The biochemical nature of this reversible mycotoxicosis is discussed.