Since the demonstration twenty-seven years ago by Ravaut1of the fact that the spinal fluid was abnormal in a high proportion of patients with untreated early syphilis, the significance of such abnormalities has been the source of much speculation and debate. On the one hand, it has been contended that these cytobiologic changes were usually transitory, that they tended to disappear spontaneously, and that they were of little prognostic importance. On the other, it is felt that they represent the actual objective evidence of invasion of the nervous system by the spirochete, and that they are the forerunners of clinical neuraxis involvement in later years. So far, little careful work on this major problem has appeared, most of the published papers being based on opinion alone or on the study, often inadequate, of a small number of patients. We present evidence, from the course of the disease, in 123