An outbreak of Malignant Catarrh was confirmed among a herd of Père David Deer (Elaphurus davidianus) at Whipsnade Park. This is of very great interest as although it is a common disease in Africa it is relatively unknown in Great Britain. This disease caused severe losses in the valuable herd at Whipsnade in 1959, but fortunately did not spread to the second herd of Père David nor to other ruminant species. Investigations did not reveal the presence of the disease among the gnu, which are commonly affected in Africa, nor any other species. The affected deer showed lesions of the alimentary tract, eyes and respiratory passages, together with a stiffness of the gait. Many secondary bacterial invaders were found at post mortem, but the extensive laboratory tests of the Ministry of Agriculture, Fisheries and Food Central Veterinary Laboratory at Weybridge showed by transmission experiments, that it had an incubation period of seventeen to twenty-three days and confirmed the disease to be Malignant Catarrh.