Use of crack cocaine and exchange of drugs for sex have been identified as substantial contributors to the syphilis epidemic in Philadelphia and other locations in the United States. In Philadelphia, from 1985 through 1989, the number of reported cases of early syphilis (primary, secondary, and early latent stages) increased 551%, from 696 to 4528 cases per year. Among 2473 persons with early syphilis interviewed by the Philadelphia Department of Public Health (PDPH) from January through July 1990, 48% reported they or a sex partner used crack cocaine, and 31% reported exchanging drugs or money for sex (not all of those interviewed answered both questions). Traditional approaches to the control of syphilis that emphasize partner notification have not been effective in halting this epidemic. The partner notification approach requires public health workers to identify sex partners of a person with a sexually transmissible disease (e.g., syphilis) and then to contact these sex partners to provide examination and curative or preventive treatment. However, because persons who are involved in the exchange of drugs and/or money for sex often cannot or will not provide sufficient information about sex partners to enable public health authorities to locate those partners (2,4,5), alternative case-finding methods are needed. This report describes efforts by the PDPH to identify persons infected with Treponema pallidum by using serologic screening at locations where crack cocaine is used.