The clinical and haematological changes which occurred in 18 Bali cattle (Bos javanicus) experimentally infected with Jembrana disease are described. The major clinical signs were an elevated rectal body temperature persisting for 7 days (range 5 to 12 days), lethargy, anorexia, enlargement of the superficial lymph nodes, a mild ocular and nasal discharge, diarrhoea with blood in the faeces and pallor of the mucous membranes. Not all of these changes occurred in all affected cattle. The major haematological changes included leucopenia, lymphopenia, eosinopenia and a slight neutropenia, a mild thrombocytopenia, a normocytic normochromic anaemia, elevated blood urea concentrations and reduced total plasma protein. The mortality rate in the experimentally infected cattle was 17 per cent. The similarity of Jembrana disease to malignant catarrhal fever and to diseases of cattle associated with Ehrlichia is discussed.