In recent years there has been a resurgence of syphilis in the United States.1 Reported cases of primary and secondary syphilis rose from a low of 6,399 in 1956 to 22,969 in 1964, with nearly half of the recent cases occurring in teen-agers and young adults. Reported cases of infectious syphilis among teen-agers have increased by more than 213% since 1956. Apparently there are many additional cases which, for various reasons, are not reported, and a consideration of these raises the probable number of cases in 1964 to more than 120,000.2 Thus it seems timely to consider both the interpretation of serologic tests for syphilis and the treatment of this infection. Consideration of Serologic Tests Although there have been a number of changes in the serologic testing and therapy of syphilis since a publication in 1961 by one of us,3 much of that basic information is still