A series of unexpected deaths and unthriftiness was encountered in red deer at Glensaugh Deer Farm, Kincardineshire, Scotland, in the autumn and winter of 1975--76. Occurrence and gross post mortem findings suggested a common etiology but microbiological, helminthological and histological examinations indicated that the syndrome was not of infectious or parasitic origin. Some of the lesions suggested an irritant poison. Foxglove plants were found in the pasture and their poisonous potential seemed to fit the post mortem findings and clinical signs. The diagnosis was confirmed by chemical analysis of tissues and botanical examination of rumen contents, and a similar fatality was produced in a penned red deer by test dosing with powdered foxglove leaves. Possible control and treatment are discussed. It is concluded that foxglove poisoning may be an occasional hazard in the husbanding of red deer. The history, clinical syndrome and gross post mortem findings may be sufficiently characteristic to allow a provisional diagnosis to be made in the field.