Abstract
Spirochaetes were recognised in the large bowel of 57 of 59 baboons as a basophilic fringe at the microvillous brush border of the epithelial cells. Both caecum and colon were usually affected, but seven animals had spirochaetes in the caecum alone. Examination of three animals by transmission electronmicroscopy revealed only one type of spirochaete; ring forms and cross-walls were present. Inflammatory changes were not seen in association with the infection, and the distribution of spirochaetes in 10 animals with soft or diarrhoeic faeces resembled that in normal animals.