TWENTY months before the time of this report, in November 1946, we began to treat persons known to have been in contact with patients who had infectious syphilis in an attempt (1) to prevent the development of the disease in these persons, (2) to reduce the spread of the disease to others and (3) to reduce the incidence of reinfection. (The persons treated after exposure were clinically and serologically negative when first examined.) For several years prior to the beginning of this study (since the advent of penicillin therapy) we had practiced and advocated the treating of persons who had had repeated contact (marital and/or otherwise) with patients known to be syphilitic simultaneously with and in exactly the same manner as the infected partners. With this method, the results were excellent; however, we felt that the impracticality and expense of the method prevented its routine use. Therefore, we directed our