(1) An inquiry was made at the Mathari Mental Hospital, Nairobi, into the validity in Kenya of the common belief that syphilitic infection of the nervous system is rare amongst Africans in their own environment. (2) The difficulties encountered by the inquiry are discussed, especially: ( a) That arising from the presence of both yaws and syphilis in the colony; ( b) that due to apparent unreliability of the Wassermann reaction under local conditions. (3) The incidence of a positive serum reaction in the general population was estimated. (4) The whole of the male adults in the hospital were selected for the inquiry. (5) The results are presented in tables showing: ( a) Mental state and neurological and other signs; ( b) serum reactions; ( c) cerebrospinal fluid examination results, including those from the Lange colloidal gold reaction. (6) The post-mortem reports on four of the series who died during the inquiry are given. (7) The inquiry appears to allow the general conclusion that spirochœtal infection of the nervous system of the Kenya native is not uncommon. (8) Insufficient evidence is forthcoming for a decision as to whether the infection found was syphilitic, frambœsial, or from an unknown source. (9) The question has much more than medical importance in view of the possibility that unchecked spirochætal infection in the past may have been an environmental influence contributing to the present degree of cerebral deficiency found in the native by Dr. F. W. Vint and the writer, and reported elsewhere. (To the Eugenics Society on November 7, 1933, by the writer, and in the next issue of the Journal of Anatomy, by Dr. Vint.)