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