This laboratory has been interested for the past two years in the investigation of a disease, commonly referred to as “Bullis Fever,” occurring among army personnel at Camp Bullis, Texas. This disease generally appears in April and disappears in the fall, corresponding to the appearance and disappearance of ticks and Trombicula in this area. It has thus far been associated with tick bites or chigger infestation and presents clinical manifestations in some respects dissimilar to those of Rocky Mountain Spotted Fever and typhus. The clinical syndrome has been reported on by others at this station (1). It has been associated with individuals in so widely separated groups as to exclude fomites or personal contact as being responsible for dissemination of the disease, and the incidence of the disease ceases as soon as the two species of insects disappear from the camp area.