This pilot study will investigate the feasibility of conducting a large, randomized trial comparing a structural intervention to contingency management to reduce incident syphilis infections in an especially high risk group: HIV+ men who have sex with men (MSM) who have had syphilis twice or more since their HIV diagnosis. Subjects will be randomized to receive either QD doxycycline as syphilis prophylaxis or a financial incentive to remain STI free. The investigators will : 1) measure adherence to study visits in both arms; 2) measure adherence to the prophylaxis regimen; 3) measure any changes in risk behaviors among study participants and 4) to the extent possible in a small pilot study of short duration, compare effectiveness of doxycycline with that of a monetary incentive for remaining STI free.