Sheep inoculated intravenously with Trypuiiosom bviicei had fever, irregular parasitaeniia, moderate anaemia, subcutaneous oedenia, dullness, anorexia, and nervous signs followed by death in 29-69 days. Emaciation, serous effusions into body cavities and generalised enlargement and oedenia of lymph nodes were seen at necropsy. Micro- scopically there was extensive localisation of trypanosonies in the extravascular body fluids, and in interstitial connective tissues, resulting in mononuclear inflammatory reactions in the heart, skeletal muscle, skin, brain, pituitary, eye, serosal surfaces, urinary bladder, epididyniis and testis, and in generalised lymphoid hyperplasia. These observa- tions in sheep are comparable to those made in other animals infected with trypanosornes of the brucei group. Trypanosoma brucei, T. congolense, and T. vivax cause the most econom- ically important forms of animal trypanosomiases in Africa. There is rela- tively little information on the pathogenesis and pathology of the diseases produced by these species in domestic animals (l 11. Infections and diseases causcd in sheep by T. brzxei occur naturally (2, 131, but there is little informa- tion on either the prevalence or the pathology. Sheep, however, have been used extensively in the past in investigations of the virulence of various human and animal isolates of trypaiiosonies in the brucei subgroup. Many of these isolates were associated with severe diseases characterized by ema- ciation, subcutaneous oedema, enlargement of lymph nodes, and corneal opacity (I, 3, 71. The present report is based on studies in sheep experimentally infected with T. brzrcei. This was part of a major investigation of the pathology of the diseases caused in ruminants by T. brucei, T. vivax, and T. congolense.