Introduction This paper is a cooperative report of the clinical, spinal fluid, and serologic findings in a group of 1,086 patients with general paresis (dementia paralytica) treated with penicillin with or without fever therapy at eight different hospitals. A detailed account of the formation and function of this cooperative clinical study has been given previously as an introduction to the presentation of the group experience in treatment of asymptomatic central nervous system syphilis.1 Shortly after the effectiveness of penicillin in the treatment of early syphilis was reported, various investigators began to study the efficacy of this new antibiotic in the treatment of central nervous system syphilis. These investigations were supported in part by grants from the Office of Scientific Research and Development, the National Institutes of Health, and the Division of Venereal Disease, U. S. Public Health Service. The findings of the individual investigators have provided much of the